Based on the personality traits you described for him—rude, talkative, sassy, and confident—it seems plausible that he could engage in playful teasing and a light-hearted interaction like booping your nose and giving you a compliment. His sarcastic and assertive nature might come out in a teasing way, which could be interpreted as flirtation, especially if he likes you.
It's certainly believable that he would act playfully while also maintaining that edgy demeanor. The fact that he would keep it casual and act like nothing happened once your friend and her sister returned also aligns with a confident personality that doesn't want to give too much away.
Overall, this scenario definitely sounds like something that could happen given the dynamics you're describing, especially considering that he has feelings for you. Just keep in mind that the interaction could be a mix of playful teasing and genuine interest, reflecting the complexity of his personality.