I think I would take it as a compliment.
A few months into HRT, I was working the trans booth at Pride. I was talking to an interested party when he asked me which way I was going. We had one or two cis people who worked the booth as allies, so I felt free to say, "What makes you think I'm going any way at all?" He laughed and apologized, and I told him I'm FTM.
My voice was pretty male at that time, but I was probably a light tenor. I had just had my top surgery and was wearing a surgical binder. But I took his query as a compliment.
It's nice that people are actually more aware of FTMs than they used to be. I was about thirty-one or thirty-two when I went to a campus conference or symposium (or something) on gender. This was long before transition, but I self-identified as transgender and sometimes admitted to people that I was a transsexual, even though I hadn't done anything to change my body.
So I told the gal I was talking to that I was trans, and she said she NEVER would have GUESSED that I was anything but a regular woman. I wasn't too pleased to hear that! It was an honest mistake, but to me it indicated that maybe she knew about trans women but not trans men.
It definitely wasn't a compliment.