As I understand these things, it's much more likely the ransomware was already on your machine though some malware you had installed or an email attachment -something with an exe file involved.  Be careful of that when you rebuild your machine.

after i check the nyaa source, it does look like the Submitter: qwert has stop doing encode anime since his last post on 2019-09-15.
he does encode lot of anime. but even this nyaa site batch never get bad command about virus. so the source of virus/ransomeware maybe not coming from him. But maybe from your computer itself.

though since u have report it as a virus. I guess it's okay to remove this from animetosho website for avoiding other people ge the same result.

That's what you get for downloading random HEVC minis

if you are reading and responding to 2 year-old messages, that is pathetic. Get a life, if you can.