Don't know, the video didn't (as usual) give the full narrative.
Whether he swopped or sat in someone else's seat before they got there and forced the other passenger to sit in his original seat, I don't know.
In any case there is nothing inherently unsafe with swopping seats whether by agreement or otherwise (assuming that it did not directly cause an altercation between the passengers). The only "safety" issue I can see is the belligerence and failure to follow cabin crew instructions. Were the cabin crew instructions reasonable?. Possibly a grey area if we are to believe that one CC said no problem to change seats and another CC (likely the CSM) said no. Like Dao and the 2017 UA incident, the intepretation of reasonableness may not be as black as white as we would like it to be.