How does chess.com know if one of the people I played against cheated?

Yes I just noticed that, but I was curious as to how Chess.com figured that out?

https://support.chess.com/en/articles/8568369-what-do-i-need-to-know-about-fair-play-on-chess-com
https://www.chess.com/article/view/online-chess-cheating
The specifics of the site's cheat detection system are not something that are released.
That said, discussions of cheating, potential cheating, or cheat detection are not allowed in the general forums.
If you would like to discuss join the following club.
https://www.chess.com/club/cheating-forum
I got an email from chess.com and it said
"We have detected that one or more of your recent opponents has violated our Fair Play Policy. As compensation for potentially unfair rating losses, we adjusted your following ratings"
They then gave me 7 elo points, which made me wonder how did they determine that one of the players I played cheated? Even I can't really tell, or at all to be honest so I am curious as to how people determine if the other person is cheating or how does the website do it? Obviously this is online chess so no one can observe the other person.