chess.com will never inform players for cheating by using a engine, if you won on time, then there is a chance your opponent could have left game. So say it's a 10-0 game, after 5 mins, he's losing and lets his time run out, chess.com reports this as 'violated our Fair Play policy', which is confusing, because if you agree to play that time control, you accept the chances of that happening.
Cheating
The more I think about it, I think he had a somewhat bad connection. Therefore, he got kicked off a few times [my memory, not necessarily "the truth".]
Well, if I understand chess.com policy, bad connections are the player's problem: the clock will still tick.
If he got dinged because he let his time run out, that's a bad policy. I lost on time many times in won positions, looking for the killer move, and completely forgot my clock. I hope I didn't get evidence against me for violating the Fair-Play policy.
Please, keep the discussion away from cheating. What the OP saw was a Fair Play Violation Policy message, for a potential violation, and has nothing to do with cheating.
https://support.chess.com/customer/en/portal/articles/1444922-fair-play-policy
What is cheating in chess?
Well, apparently, it can happen in benign circumstances.
Let's take my game against "X" [I don't disclose names.]
The game was harmless enough: 1.e4 e5 2.Bc4 Nf6 3.d3 Bc5
4.Bg5 O-O 5.Nf3 d6 6.Bxf6 Qxf6 7.Nc3 c6 8.O-O Bg4 9.h3 Bxf3 10.Qxf3 Qxf3 11.gxf3 Nd7 12.Ne2 b5 13.Bb3 a5 14.a3 g5 15.c4 b4 16.axb4 axb4 17.Ba4 Nb6 18.Bxc6 Rac8 19.Bb7 Rc7 20.Bd5 Nxd5 21.exd5 f5 22.b3 h5 and Black won on time in a 10/0, 15/10/, 30/0 or some such time control.
However, I got this message from chess.com: " 'X' may have violated our Fair Play policy - it has been noted and they may have their account restricted."
Why or how did "X" cheat (in the large sense) or violate the Fair Play policy (whatever that is)? [It wasn't a tournament; so, that's taken out of discussion.]
I applaud chess.com for trying, but there is no real way to cheat.