How does Lichess determine cheaters?

I got a notification today saying that I am refunded points because I played a cheater, but when I looked at my opponent's games, it does not seem that he cheated.
So I am wondering how Lichess determines cheaters and if Lichess ever mistakes someone to be a cheater when they are actually not cheating.

lichess.org/forum/off-topic-discussion/why-have-i-been-marked-as-a-cheater-?page=2#17

Any doubts remaining?

Thanks @Sarg0n.
I'm still wondering how often an innocent person is marked as a cheater.

I don't know. An educated guess: this has never ever happened...