Well for all you know, Rick just poked his belly where he was shot. Wouldn't necessarily call it 'torture' since the dude was already in a lot of pain and scared shitless even before that point - basically it's like when you ask your buddy where you're going and he keeps going "it's a secret man!" and it isn't until you annoy the hell out of him or keep poking him or something that he goes "Alright alright already we're going to a frat party!" or something.
Guy was probably scared that Castle WOULD do something nasty instead of just poking him. Or he hit him in the nuts...
C'mon this is Castle we're talking about - he's got a dark side that's also inspired by comic books, movies and tv shows - BUT he's also got a light side that's inspired by the same thing. He's driven but he probably has it in his head that this is "Liam Neeson" moment where he uses all the skills he learned at Beckett's side to save his daughter, just like a character from one of his novels.
Although what I'd like to see is... Alexis becoming more a part of the "team" as it were. I kind of liked seeing her as Lanie's little assistant for a couple episodes there. Honestly I LOVE Alexis - she's the only "child" star that I can tolerate and I do sincerely hope she keeps the same level head she's had all this time. Doesn't either turn into another Lindsay Lohan or something. She's a beautiful girl, got a great comedic timing, as well as dramatic timing.
And frankly... after seeing her in this episode, I'm convinced that if Fox or Marvel ever wanted to do something with Hope Summers - she would be a kick ass Hope Summers.