This really happened…. I know because I was on the ride. We raced each other and 2 people beat me, suddenly their rides are flagged and a newbie to the area has the KOM.
I had a KOM (actually still have it, it’s my only uphill KOM) I didn’t even know I had until I lost it. I guess I got it when someone else flagged a ride. The person who beat me was clearly in a car so I flagged them, and now I have it.
Pro tip: if you are trying to get KOMs in a motor vehicle, don’t leave your HRM on.
Yes its fine to flag that ride if you’re sure the algorithm made an error and the guy didn’t ride the actual segment.
To me, a man taking a flatland KOM crown with motorpacing does not seem very different from a woman taking a flatland QOM crown by riding in a bunch of men who typically ride the segment faster than the QOM time. True she has to be able to keep up with them but the speed she travels at is largely determined by the group, unless she’s genuinely in the hunt for the non-gendered CR crown. The same could be said for a cyclist sitting in the draft of a fully-laden B-double. The truck-drafter still needs to have the power & the gearing to accelerate up to & hold speed with the truck.
And then, what about the push & suck effect of passing traffic on a busy road? I’m sure anyone who’s done time trials or similar efforts on a highway is familiar with that, especially from before the time transport authorities were telling people to leave a certain distance when passing. I have somewhat fond memories of the sudden & momentary tailwinds provided by a semi passing at speed about 2’ away. At what traffic density does it become too much assistance to be allowed?
Frankly I think it’s mostly a storm in a teacup: even the acronyms “KOM”/“QOM” suggest that the real value is in Mountains, specifically climbing them, where the benefit of drafting is lessened unless it’s a gradual drag. What if strava removed overall standings leaderboards for all segments that were flat, downhill, or climbing of less than 2%? The only records I have a shot at are descents, & a lot of those leaderboards don’t tell much about athleticism, but some of them do tell who’s least afraid of dying. Somehow my adrenals still think 30 years later that I’m an indestructible teenager. 
If only I responded to & recovered from training stimulus & slept as well as I did back then. 
That I’m now living somewhere that’s fairly flat & that I’m (for the time being at least) dedicating myself to z2 are probably keeping this nutter safer. 