

It was first found in monkeys, but actually originated in rodents. It should technically be rodentpox.
Also, racists and homophobes used it to create stigma against gay men. In was/is particularly prevalent in that group. There were rumours that you caught it from sex with monkeys.
Basically it was renamed to pull the teeth of a nasty and insulting use, and to break a misunderstanding on its source.
https://www.royalroad.com/fiction/55418/rock-falls-everyone-dies