misinformation has pathological tendencies. when people know the facts (ie are vaccinated) it doesn't spread. new uma fans are like erstwhile uncontacted peoples in the new world, they have zero herd immunity
then you add on content creators (superspreaders) to this mix...
honestly what IS it about umamusume that compels people to peddle misinfo like that... it's insane because you'd think that it'd stop at just the horses and the irl connections but no it goes as far as coming up with fake facts about the people that work on the game itself lol