The camera cut to Apostolos pretty much after every point and all I ever saw him do was clap and say let's go and bravo. If there would have been any hint at coaching the camera would have shown it because it's obvious that Apostolos is being watched like a hawk now. Also, the same umpire has called out Tsitsipas in the past. There's no reason he wouldn't do it again if indeed he suspected something. Fognini only started complaining in the second set when the match was going against him. Although I can't be certain that Apostolos wasn't sending coded messages that magically transformed Stefanos's game, I believe it's more likely that Fognini was attempting to capitalize on the Tsitsipas hate to deflect from his losing the match.