He was presented as having experienced a philosophical shift toward non-violence, but the result on-screen was that he was far more violent than he was in TNG.
I think what makes it funny though is that in-universe there's not really any reason for him to behead like ten people at once or w/e, he lives in a world with wide-beam stunguns and is an accomplished martial artist; subduing the guards would have been trivial. As a member of Starfleet Security, you'd actually have to go out of your way to use lethal violence, so plentiful and easily-accessible are the means to avoid it.
So the reason he gores a group of people to death is because Matalas thinks it'd be really cool to watch a bunch of people's heads fly off with blood shooting out everywhere, and loves the trope where a character gets a "cool" intro in which they kill a bunch of unnamed goons, but he's simultaneously impressed himself with his "Worf likes pacifism" idea, so the two ideas collide in a way where the entire theme is undermined before it's even introduced because Matalas' worst instincts win out every time.
It's like a microcosm of the show as a whole that's so perfect it's hilarious (a similar one: Amanda Plummer is introduced as someone traumatised by her treatment at the hands of S31, but her character's arc ends with her being brutally fired into space and killed so that MERGED DATA can have a "badass" one liner while killing her. All the potential plot is quite literally jetissoned from the show in the name of a fleeting "cool" moment of violence).
