My first thought was that he meant Bipolar NOS. Then wondered if maybe it had a new name in the DSM 5. Well, turns out it does have a new name, but it's -- "Otherwise Specified Bipolar And Related Disorder". (What a cumbersome name! They never seem to make a name simpler!)

I'd guess he's referring to that situation, but just using the word "atypical".

If this is so, it is easier to describe via its previous name, so I will use that. The NOS meant "not otherwise specified", which described a situation where the symptoms seemed to reflect bipolar, but didn't fit neatly into either BP 1 or BP 2. It is also a term (whichever name it goes by) that is often found in a situation where the provider hasn't known the person long enough or for whatever reason doesn't have enough information to make a determination of either BP 1 or BP 2.

This means that it might be a temporary dx (pending further info) or a dx in and of itself where considering full information, symptoms simply don't quite fit either BP 1 or 2.

Does that make sense? The only way to know for sure if this is what they meant is to ask of course. But in the meanwhile, I think this is a pretty good guess.