Yes, they are in fact hallucinations when there is no source possible for the given smell. The strong scent/memory experience is a totally different thing, universal and "normal".

Personally, I'd not overthink occasional incidents or when they are a variety of smells. From what I've read, it seems that they tend to be consistent in the type of scent one experiences (eg. rotten flesh, burning rubber etc.) Olfactory hallucinations can occur with BP, but there are many other potential causes, some mental, some physical.

I do have olfactory hallucinations, and have had for years (17 years in fact). There is no consistency for when or where they will happen. Trippin', I totally feel ya, as mine are the smell of rotten chicken. It's disgusting. Fortunately, they only happen periodically.