The language is very clear here. You shall park your bike no less than 45º and no more than 60º. Not sure if you took math or not, but 0º is not within that range. This isn't even about exceptions.
It is about exceptions, and it's about how rules are written, not math. That's why it's an exception and why it says "may".
You park parallel to the curb, OR you may park at an angle within the prescribed 45 to 60 degrees. Don't know what 45 and 60 look like? Then park parallel.
The idea is probably that you park parallel, or you park on such an angle that it allows other bikes to park beside you without going so far as to be close to perpendicular, which could make it difficult for a closely parked two-track vehicle to get in or out. That of course, is just my opinion based on keen observation of what is actually accomplished by parking at between 45 and 60 degrees from the curb.