Is it just me, or did I just flag a post as both Offensive and as Not an Answer?
Is that a bug (as I thought this wasn't possible before), or
was I just being too awesome is it by design?
"Offensive" (a flag/vote) is handled separately to "Not an answer" - so this has always been possible. The hint in the UI is subtle:
Basically, "not an answer" is implemented as a pre-populated ♦ moderator message. This means that yes: you can indeed do both (one flag/vote, and one moderator message).