It is an answer.
An answer has two (and only two) essential elements:
- It addresses the question
- It attempts to solve the problem the user has
This answer does that.
It directly addresses the question, and it tells the user something that could possibly be the problem.
That doesn't mean it's a good answer -- but flagging as 'not an answer' isn't meant for those situations. That's what downvotes and comments are for.
If you had flagged it as 'very low quality', I could have seen marking that as helpful (deletion is another story, but it is at least a helpful flag).
I see a lot of
Not an answer flags used because the answerer is unsure of their answer and pose their answer as a question. They're still answers, regardless of the level of confidence the poster has in their own answer. If you can replace a
? with a
. and it still reads as an answer, then it's an answer.