On the video it looks as though less than four seconds passed between the "clear" radio call and the airplane actually being clear of the runway. That would have required some spectacular acceleration, from the departing aircraft, to even come close to catching him.
True but what-if P1D had a sudden stroke right there and was no longer able to clear the runway? Anticipated separation is permitted at controlled airports because the controller can issue an abort if separation cant be maintained... Who was going to tell that taking off airplane to abort? Even recognizing that the plane departing wouldn't need the full length of the runway.
I'd counter the argument that it was just 5 seconds with how exactly did announcing clear 5 seconds early really make a difference to the departing/waiting aircraft?
No P1D got caught by a student pilot being sloppy and rather than admit it was sloppiness on his part, he doubled down on it being "quality airmenship" because he was "situationally aware" enough to get that plane behind him rolling.
P1D broke the cardinal rule. He started communicating before he was finished aviating. He was also running through his after landing checklist while still on the runway and on the move.
I realize of course these and other faux pas are minor issues and easily downplayed as non-issues. We're all guilty of it at times but we generally recognize it to be sloppy and/or error prone. We all would generally recommend that you not do it, especially to a new student pilot. We should strive to do better and practice what we preach.
In my opinion, P1D chose to post his videos to youtube, he chose to be subject to this scrutiny. If his response to being caught doing something that isn't by the book is like it was to this kid, a condescending "I'm uber-pilot with 1000's of hours so I'm right and you and everything you've learned as a low time student pilot is wrong because I have situational awareness so I dont need to explain myself or what I was doing to the likes of you" which may not have been his intent but having read his initial response a dozen times in every POV I can come up with, that's how it consistently comes across, I mean he didn't even answer the kids question, than maybe he shouldn't be posting videos on youtube in the first place.
If his response to being called by the FAA to be told "hey we received a complaint, we reviewed it and you're all good, we just had to let you know we got the complaint" is to use his platform to attack and denigrate another pilot for their own faux pas of involving the FAA for something so minor and to name names so his followers can predictably go after the young man, than he definitely shouldn't be an online representative of the pilot community.