So I recently got with a girl I met off tinder, after a few nights of going out and playing around I decided to make her my girlfriend. We both let each other know that we're looking for something longterm, and one of the things that I like about her is how strait up and honest she is l. She isn't afraid to tell me how many partners she has been with or what they did. The problem comes up 2 days after I told her to be my gf. She needs to return one of her longtime friends clothes back to her and so I agree to go meet her friend and family. We go there, chill and smoke for a bit, when all of a sudden my girlfriends friends' brother comes in. He's pretty chill at first just joking around and shit, but then he ramps shit up. He starts asking me questions about my gf like, "what did you see when you first saw her?" And "what did you notice about her body?" Obviously I didn't feel comfortable answering these questions in front of him and everyone else, but each time I tried to evade, he just kept saying "what do you have to hide?" This continued for a while all the more getting more intense and invasive, while cracking a hella unfunny jokes. Eventually he finds out that we net on tinder and so he asks me to pull out my tinder profile so he can see my profile pic, I didn't want to, but if I didn't it would have looked like I was trying to hide something, so not only does he show everyone in the room that I still have tinder installed even though I have a girlfriend, he also makes hella fun of my pictures. Now I know alot of you guys must be asking "why didn't you just not answer?" Or "why didn't you ask him why he wanted to know?" But this guy was different. I have never met someone in my life who can twist words around like he can. I can't really explain it, but he seemed to turn everything I said against me. After we were done talking i asked my girl what the hell was that about, and she just basically apologized and said he grilled me because he cares for her and wants to make sure she's with the right guy. She said that she expects me to talk to him again. I let her know that I'm cool with his family, but I don't ever plan on seeing him again without things going hostile. What should i have done in the situation. What should i do now?

TLDR: I got grilled by one of girlfriends family friends, and I want to know what I could have done differently