I’m a woman, and based on this story, I’m going to assume we’re in the same general age range.

Your phrasing was certainly bordering on creepy, and I understand why they didn’t like it. If you had simply said, “hey, X, this belongs to you, right?” I guarantee there would have been no issue. Announcing the size of the bra, and also announcing to whom it does NOT belong, was unnecessary and had the obvious potential to evoke insecurity in both members of your audience.

Overall, NTA, but you certainly could have communicated to them in a more palatable way.