Is it normal for brother to ask about my penis?

I'm the eldest of 5 younger brothers. We grew up pretty close and as the eldest I was always the one they looked up to the most. I always felt like I 'should' be the best role model that I could possibly be. I feel fortunate that my brothers have always felt comfortable talking to me about things that they wouldn't share with anyone else, even our dad. I always been the 'go to' brother and as so I have always taken that responsibility seriously. When asked about certain things, friends, girls, sex, drugs, and whatever, I have always answered honestly and tried to be non-judgmental, but more educational, informative, but still directing them in a 'better' direction. I admit that there have been times where I have been surprised at what they have asked me, but I always play cool, as I never want to make them feel awkward or uncomfortable about speaking to me.

So my youngest brother is 14 and very introverted, not many friends but pretty smart, compassionate, sensitive and always sincere. I was home visiting and we were watching TV on the sofa. Apparently I was wearing shorts and sitting in a position where the leg of my shorts were open and my penis was visible to him. I wouldn't have even known unless he had mentioned it.

Him: 'Hey, I can see your dick.'
Me: 'What?'' I look down and rearrange myself, and being playful I say, 'So stop looking foo!'

Now growing up with 5 brothers, all pretty close in age, you can understand that we have all already seen each other naked plenty of times. We shared a jack/Jill bathroom and our father would take us to the city swimming pools during the Summer. So changing together and seeing each other naked was very, very normal. However, as he is my youngest brother, he is the one who I have spent the least amount of time with. He was in elementary and I was in H.S. Now he's in H.S. and I've moved out.

About 10 minutes later, while watching the movie or whatever it was, he says, ' Hey, can I ask you a question?'
Me: 'Yea, what's up?'
Him: 'Would you mind if I could see your penis again for a minute?'.
Me: 'WHAT?! No!', I'm laughing and dismissing him. 'Why would you want to?!'
Him: 'I'm just curious...that's all. I just want to see it.'
Me: 'No, I don't think so.'
Him: 'Never mind, I'm sorry for asking.'

He turned away and then a few minutes later he left the room. He didn't make eye contact with me for days. When I tried to talk to him he seemed embarrassed and avoided me. I felt like crap and l feel like I've placed a wall between us. I don't know how to make it right.

I believe I made the correct decision, but I didn't mean to embarrass him and I didn't intend to make him feel like he couldn't talk to me. I suspect he may be gay but I really don't know that for sure yet.

So my question, is it normal for him to be curious? Personally, I think curiosity is normal for teens going through puberty, I know I was, but is it normal for him to ask me, his brother, to show him what I'm packing? I feel like I made the right decision, but in retrospect, he had probably already seen me naked like 100 times. Would it have been so terrible to just comply? Just pull it back out and let him examine it for a few minutes? Get his curiousness out of the way and just move on? I don't know.

We're a little better now, but he's still way more disconnected from me than before. It kinda sucks.