My understanding is that anything above 50 cc IS a motorcycle across the board in the US, with all the benefits and responsibilities to which you yourself have been entitled. I agree with you that the patrolman was incorrect.
If he was the only cop in the state, that would be grand! But he isn't. Here in Mass. I have run into the same type of misunderstanding, where one or two officers have been determined that my ET2 doesn't look like a "moped" and therefore isn't. They are wrong, and the RMV (DMV) will back me on this, but I always worry I'll have to spend valuable time straightening out a misplaced ticket because of it. Fortunately for me, every cop in Boston DOES know the distinction except for those one or two.
Your friend might run into the same police demographic, but it would work against them in that case, with most police correctly giving a ticket to an unlicensed motorcycle rider.
The web sometimes IS no help, but I am sure a call to the state's DMV will make things clear (most likely far faster than an in-person visit

)