An abusive partner accusing the other of cheating is very often a projection of the fact they themselves had been cheating. Since they know they would cheat, and were/are, they either assume the other person is the same way, or simply don’t want to draw attention to their affair. It’s an awful thing.
These talking points sound like those of Thor from pirate software. I hope that’s not who you got this opinion from, because that man is just an industry shill.