YTA , but I feel by mistake/misunderstanding, not intentionally. Cant stress enough that i dont think you were intentionally being a dick. We all do stuff that we think is kind hearted and funny, but turns out to be hurtful to someone else. It happens, but what matters is what you take from the situation afterwards and I feel this post alone shows that your self reflecting and desire to understand their side of the conflict better, so as a whole, NTA.

Personally, as a woman myself, that text would have made me feel objectified in the situation you described. I, again personally, would have felt hurt and upset that after a nice video call getting to know each other the moment that stuck in your mind the most was an accidental glance at my breasts and that it then lingered in your mind enough to text about it, especially early in a relationship where intimacy may not have been explored, yet. In that situation, i would have personally hoped details about me as a person, not my physical being, stuck with you first and foremost.

Parts of her physical being were shown that she didnt mean to, or wanted, to show. As a broad take with nuance, I feel that if someone sees/hears/learns something, accidental or not, that they clearly were not supposed to have known about, and that information violates someones sense of privacy and/or autonomy, then they need to treat that information as if they never had it in the first place. I feel it can almost be compared to HIPA policy in the U.S. where medical professionals legally cant discuss your medical details with others without your approval. I know my doctor has seen my bare body, but I trust that they wont share with others what theyve seen or discuss with me details about myself that dont align with the medical-based relationship i have with that doctor (i.e. saying he feels a lump in my breast vs my breast feels soft).