I find answers in this format annoying. Why not? Maybe he's never heard of it. Great answer, but let's not assume he's considered it and decided not to.
I think you came across as friendly and helpful. To me "why not" is a gentle suggestion, and not a literal question. Maybe that changes in different parts of the world?
Colloquially "Why not?" is used to make a suggestion. That is, "Why not" means "Perhaps". One need not trace or question preceding statements or ideas nor is there any need to be annoyed.