because they accidentally got a pre release version of magic the gathering?

It was a streamer that got the pre-release boxes early by mistake, and live-streamed opening them to drive traffic to his channel. Most cards aren’t revealed ahead of time so these leaks let potential pre-buyers see what was in the set and decide if they wanted it.

What he did was stupid, but he did nothing wrong, and nothing especially harmful.

Calling the Pinkertons on him was obscene on principle, but it was especially egregious when the damage was so minimal. They hurt themselves more with that stunt than the leaks hurt them.