Unless the displacement is under 50, in which case it may count as a motor-assisted bicycle after all.
Either way, it's definitely not a bicycle. Some cops may not really have that section of the HTA memorized and assume that they're treated like e-bikes, but all it takes is one cop in a pissy mood who knows the HTA to royally **** you sideways for riding your homebrew buzzer.
I was looking at my buddies. You have to pull in the "clutch" and pedal, once your moving you let the clutch out and it starts the engine. So in the eyes of the law it would still not be a bicycle even if it's under 50cc.