My Mrs got a cut inside the ear and didn't even know how she did it. Getting whacked in the head by an 19 stone dude would certainly be one way it could happen though. (To Wilder, not my Mrs. I hope).
Ears tear fairly easily. You see it in wrestling, rugby, etc. Maybe not as much in boxing because they don't get as much contact.
Wilder has had excuses in every fight he has looked bad in, and has given a stupid excuse for this one. If he had a real reason why he looked so poor he'd be on Instagram right now with a doctors note.
Finally, as Royal Watcher pointed out. If his ear drum is burst, then it happened because Fury punched him. The objective of boxing is to punch your opponent until they can't continue. So, job done.