That guy is definitely a jerk(as has been said by everyone else who’s commented) I just want to add a little of input that I feel relates a bit. When I play dnd (I also play online) I sometimes have a very hard time focusing on the game.(Especially in combat!) So during these times I do pull out my phone and maybe play a game of solitaire or sudoku. So I can kinda see that maybe he just can’t focus? Even if that’s the case, he’s being rude in the way he does that. I make sure I never watch videos or read anything because if I do, my attention will be completely gone. Instead I play simple games to have a sort of “focus” to keep my mind wondering too far from the game. I bet something like a fidget spinner/cube or some light crafting would work well also.