No, Bob could say whatever he likes about himself, but it would not be out of line to ask why Bob would say that.
Is Bob depressed, does he have a low opinion of himself because it is true, or because someone else has instilled this mentality in him. Does Bob need help? Who is Bob? Was he serious?
These questions are not out of line. The other difference is you are giving a direct quote from someone. We are talking about interpretations. If you gave me an interpretation of what Bob said, I may ask to find out WHY you interpreted him in such a manner, are you correct in said interpretation, was it painted by personal feelings? Maybe it could be interpreted differently.
So questions on a topic you speak about in a public forum is not an unfounded thing. You say things in a public forum, people may question it. Simple, nothing more. You can answer questions, or you can ignore them. Either way.