This was also my take. You (or rather,
@luke511 ) finds a twitter feed that has been set up with the sole focus of finding any footage that can be used against McTominay; it is the literal definition of agenda posting. The one he posted after the Villa game (I think it was Villa), there was a clip where McTominay receives the ball under pressure, turns two opposition players and then dribbles past a third, hits a switch to the opposite flank (not a great pass), but the receiver slips and it goes out for a throw. You could take the first 10 seconds of that (him taking on multiple players) and make him look like a world beater. Or you could do what that twitter thread and the agenda posters did, which is to cut out all of that and just show the pass (which even then wasnt solely McTominays fault).
The groupthink in this place has been problematic for a few years now. A given line or opinion gets repeated enough times that people just take it as fact, and use confirmation bias to try to justify it. Its willful ignorance and mental gymnastics at times.