Lol I never took a class, I just have a book and the first thing it taught was a version with just three.
So it's probably wrong, just the easiest version possible.
I got in trouble once for playing anime themes on a piano at an anime convention. Apparently, the venue charges extra for a piano, and the convention had elected not to pay that because it's stupid. The location left the piano out anyway, though, and there were no signs, so how was I supposed to know? Luckily, the staffer only gave me a warning and then decided to guard the piano to dissuade others.
So it's probably wrong, just the easiest version possible.