would not be my defense because to me it clearly is not part of a bathroom group.
Let me respond to that as a rhetorical exercise in code reading, which may be a tangent and not particularly helpful to the OP.
The way I read codes, the fact that the name includes the word "bathroom" doesn't mean anything. You just look at the definition and apply what the definition says. If the code writers went through and changed every use of the term "bathroom group" to "purple group," it would have no substantive change to the meaning of the code. So if the fixtures that compromise a bathroom group are all supposed to be in bathrooms, or maybe even the same bathroom, the definition of "bathroom group" would say so.
Let me also point out some potential undesired consequences of the interpretation that "bathroom group" fixtures have to be in bathrooms. The relevant UPC definitions are:
Bathroom. A room equipped with a shower, bathtub, or combination bath/shower.
Bathroom, Half. A room equipped with only a water closet and lavatory.
So now suppose you have a toilet room off the room with the shower and lav (the bathroom proper). That toilet is no longer in a bathroom; does that mean it can't be part of a bathroom group? Horizontal wet venting is restricted to bathroom groups, so does that mean the toilet can't be horizontal wet vented?
All of this is just to say that the broad reading where you just consider the types of fixtures involved, rather than wall locations, makes much more sense to me.
Cheers, Wayne