Stranger than a bunch of professional soldiers shooting each other when in an irreversible position and the enemy is routed? Not so much. Friendly fire perhaps. At the time the majority of vehicle ambushes will have been UKR forces on Russians.
Plausibility, there isn't any in that story. Sorry.
This literally happened to TF 1-41 in Desert Storm, TBF. The Iraqis routed and three US battalions of highly professional troops started shooting each other. They only avoided wiping each other out because it was three battalions and not three rifle teams.
This story just sounds like a counter-ambush being done by UKR special forces though, if it happened at all, because as you say it could also be entirely made up. There's plenty of that going on in both Ukraine and Russia, and it wasn't more than a few months ago that the Russians themselves were accusing the Ukrainians of the ones being given super psycho soldier stims or whatever that "destroyed all traces of human consciousness" because the RT storyline ticker rolled over back to "American-run bio-labs creating genetically modified super-soldiers/anti-Slav viruses
(COVID)" from the March 2022 season arc. Reruns smh.
I'd wager on the side of fantastical invention given the source (a random email?) and the fact that Ukraine has proven especially savvy in playing media with stories through literally hundreds of hired-on PR firms astroturfing stuff like this. Saint Javelin, which was commissioned by a Canadian-Ukrainian journalist running a five-man PR firm in Toronto to a Korean artist, is one example of the astroturfing going on.
As a side tangent, one especially amusing story, which I heard from a friend who was in Odessa recently, was that the Ukrainians (or rather, the people there were relating rumors to friends and family, thus I guess the local TDB and hospital workers in this tiny hospital in Odessa), back in April or May or so abouts, thought that the Russians had captured Chernobyl for purposes of trying to remove the "cap" over the sarcophagus to "release the radiation". When my friend pressed the guy on the means by which they would ensure it wouldn't blow back onto Belarus, he was told rather seriously that they had setup "giant fans" to blow it back onto Ukraine and contaminate them with radiation. It got a chuckle out of him once the guy had left the luncheon.
This same friend also got extorted by a Ukrainian territorial defense captain on a voice call with me and a couple other guys for something to the tune of $800 USD (don't worry, it wasn't his money), but he got them back by nabbing a couple Starlink terminals, which were used for the ambulance service he was working with. AFAIK the Starlink terminals are still being used by the ambulance folks based out of Chisinau or some other place in Moldova. Tangent over.
That said, if that story happened I suspect it was just a counter ambush by NODS equipped Ukrainian special forces, who presumably just kinda left afterwards, so perhaps they were a reconnaissance section or platoon of the incoming airborne brigade. The reason no one found anything is because they didn't check 50 meters past the bodies and find all the shell casings of the counter-ambushers, or the commandos were using brass bags, or whatever. That's the only thing that makes sense I think, since we know the Ukrainian commandos were pretty active even in the start of the war. If they're operating on Soviet training, they will be operating far forward, several hundred meters off the main route of travel, and independently, in small detachments of main bodies, as a reconnaissance vanguard, at least in wooded terrains. This is how said friend worked with the 876 BTG as a reconnaissance vanguard trooper, among other things, as he was 876's tactical SME and occasionally part of the special reconnaissance company of Marines, in 2nd Chechnya.
He got handed five guns back in Odessa simply because he was like one of maybe three people there who had been in significant combat, in a big scrap like 2003, that wasn't Afghanistan or Iraq occupation. Not that he used them, but he did see a couple Mi-28Ns and a Russian Su-27 at the time.
Given the 79th Airmobile Brigade is considered one of the most elite formations of the Ukrainian Army, it would absolutely have special forces attached to it for that purpose, too. These were literally the guys doing all the deep raids in March and April, and in 2014 too (the brigade, I mean), after all. If they heard gunshots they'd just go towards them, neutralize the ambush, and move on with their actual job, whatever that is. It might as well appear to be divine intervention to a lowly lieutenant or something. The dude I know rescued a couple POWs from Chechens, after finding a mortar battery (not destroying it, because it was needing to be located for an air strike), and got word about the POWs being broadcast out of a ersatz TV studio or something, so they rolled up and zapped like 60 guys who came out of the bunker with grenade launchers and PKMs. A cool guy.
Supersoldier drugs it ain't but Jacob's Ladder is still a good movie. Good to see people still reference it now and then.