Would I be wrong for asking my MIL the truth about something my husband won't tell me

My husband and I have a really great relationship. We have been together since we were both 18. We're both 31 now. We don't have or want kids and honestly just want to be with each other. I felt like our relationship was always strong but I just recently found out he may have not told me everything about his life. Me and him are going on a trip to Las Vegas. We figured it would be fun and are going with a group of couple friends. My husband's older brother was here and they were smoking weed together. He hadn't told his brother about our vacation yet and when he did his brother just stared at him and he goes "Vegas? Really?" My husband says "Shut up." His brother says "That just feels like a trauma reminder." My husband said "Shut up. It's not going to be like that again." And his brother says "Okay. I believe you. Plus we're older now." I asked what he was talking about and my husband said "Nothing." My little brother was also there and my little brother is 15 and he also asked what this was about and my BIL goes "Dylan. Just gonna tell ya. If you ever go to Vegas. Do not go alone as a teenager, lie about your age, and then accept rides from strangers. You may end up a little traumatized by the end." My husband says "Can you shut up." I said what is he talking about and my husband said "Nothing!" He snapped on me. I asked again after giving him a few days and all he told me is he and his brother thought they knew better than their parents were they were teenagers. Made some stupid choices and he learned a very difficult lesson and very traumatic way. He's not giving me any real answer as to what his brother was talking about. Sounds like they just got in trouble in Vegas when they were kids but won't be tell me? I feel like his mom might know and I really am thinking of asking her? Would that be wrong