Wouldn't that also fall under NG+? The rules don't specify as such and assumes you can play on a new file, with only a randomizer on the final 5 levels.

Technically yes but..... On NG+ you can choose any master for any level, on RNG% you use the random button and let the game decide every level. For both its a new adventure game file but for an existing user with the masters unlocked , any% is a new user Single master is also technically NG+but specifies you stick to just one, free choice should be fastest