I think that it's perfectly normal to wonder how a mate compares to you statistically, in all ways, from height to weight to biceps size to genitalia. I've not got many mates whose flaccid cock size I don't know. Likewise I know with most of them who is cut and who isn't. I'm sure that they are familiar with my stats - although there are very few that are open enough and relaxed enough to discuss it together. It's no big deal, though, and curiosity is nothing to be ashamed of.
I know that one of my mates and I are virtually cock twins. I found that out after we'd been swimming and were drying off and changing together one day. We are (or were, no idea in recent years) identical (soft) in almost every dimension.
I did have one mate, though, for many years, who I used to spend many hours with. We'd go out in the evening drinking and often stand side by side in a park or behind a building and have a piss on the way back from the pub or club but we never saw each other's tackle as it was dark. We often slept over on each others floor but again never saw each other as we slept in our underwear. I never really saw his cock until the very last time that I saw him, when was at the pub during a catch up with the group that I was at school with. We both ended up at one point standing at opposite ends of a trough urinal together. He stood fairly well back and we turned towards each other as we chatted, whilst pissing. I had always assumed that, like 95% of us, he was uncut. However, out of the end of his hand, the head of his penis was fully visible, clearly uncovered. It was impossible to see whether or not he actually was circumcised, as his hand covered his shaft and the rim of his helmet, meaning that I couldn't see whether he had a circumcision scar or his had his foreskin rolled back under his hand. I still wonder to this day, when I think of that night, whether my best mate for all of those years had actually been circumcised. Sadly, due to work, location, life etc. we drifted apart and haven't seen each other since that night, which is sad, considering that as teenagers we were inseparable.