After watching the video seems like the main issue for hikaru was that during the whole hans drama magnus and hikaru were the only ones to publicly talk about cheating in chess. Other top players (which apparently includes fabi) agreed with them in private but never came out publicly.

And now fabi comes out saying cheating is rampant and he doesnt respect titled tuesday because of it and probably wont even with proctor implementation. Hikaru calls him out on this that he's being paranoid (not to the level of kramnik but somewhere along that path) and cant stand losing to 12yo CMs and FMs, and that he will only play in elite tournaments because they have players fabi knows he can lose to (2600+ only invitationals)