Diaco's pulling a reverse Lou Holtz. Holtz had a team that was going to be favored in every game, often heavily, and used his press conference to build up their opponent so that after they won the perception was "hey that was a decent win". Presumably the comments plus his locker room talks were aimed to instill in his players that they need to take their opponent seriously and stay focused. With Diaco, his team is going to be the underdog in most games and he needs to get the fanbase engaged so they'll show up, and his players to buy in so that if they lose a couple games they don't give up like last year.
At least on media day, I prefer this enthusiastic approach to the typical kind of coachspeak, of which Bellichick is the extreme example. How it plays out over the season which in reality will probably result in a small number of wins, remains to be seen. It could backfire. But I think Diaco is thinking about the next 2-4 years and this is probably more for setting the tone for next year and beyond than it is for this year.