I think he has just gotten used to getting up at that time. Mine will wine to get up at 6 am...which is fine on work days
. But once and a while something happens and they will wake at 4...then the next night the same... And before you know it the internal clock is set. It happens to us too ( that is why I am on yt ay 6:40 am on a Saturday morning lol) you may be right in that it was the cats who started this...and he then go attention from you.
The question is how to reset? If you take him out and put him back and he whines.. For how long? Will he wake others?