Curiosity is healthy. There is not a thing wrong with asking about something you notice.
Your asking is about your curiosity.
His replying, or not replying, is about him. A therapist may choose to answer or not, or not at that time, if they think aswering or the answer might interfere with the therapy process.

My therapist has a grown daughter. She mentioned her early in my therapy. I didn't ask personal questions because I didn't want to know a lot about my therapist when I first began with her. One year around Christmas my therapist was going to take a week off, then her plans changed. I asked something later about her plans changing and she replied "We decided...". .. "We?" .. hmm. She doesn't wear a ring. So, brave person that I am... a few sessions later... I ask. Who is the other part of "We"? I was so expecting an answer because it was a rare personal question. (As if that meant she "had to" answer, as if she is not a separate person who chooses whether to answer a question or not, based on her own thoughts and feelings). So I asked and she said she was choosing to no answer that, but wanted to talk about my being curious and what I imagined the answer was. (Adding to the process, rather than distracting or interfering). So that's what happened with me. Much later she casually mentioned her husband, so her choosing to not answer was about that very moment when I asked, and about my asking, my curiosity.

Anything and everything is to talk about in therapy.