Yes. If it’s clear that the observer means for the observation to be of a certain subject in the photo, then you should ID that subject (if you can). If it’s not clear, then ask them. I don’t think they effectively “lose control” of the subject if they don’t immediately make it clear upon upload.
I’m not sure there’s a significant downside to letting an obs go unidentified here or there, aside from it being tough for the fastidious among us (meaning most IDers, including me) to accept. To me, the person uploaded a photo of something they wanted to share and get IDs/comments on, and we shouldn’t decide what the subject is (in ambiguous situations).