I used to doodle a lot more---but yes I doodle. Now I call them my sketches
Even so, I find that study hard to believe. I know that when I pay attention, I take copious notes, and I'm pretty sure I will remember more than a 'doodler', because I was really focused on capturing the information that was being imparted. But that's just me.
I also don't quite agree with the idea that when you're in a class listening, it's not stimulating enough so your brain needs something else. I think, sometimes, no matter how great the information being shared can be, your mind just wanders anyway because it can only take so long of a person's voice droning on, or you may be tired, or have a lot of other things to worry about at the time...I don't see how doodling helps you take in that class better.
I guess it may help in not totally canceling out what you're trying to retain, but I think people just get restless sitting at a desk for very long and need to distract themselves with something else after a while. For myself anyway, if I doodle during a class, I usually get carried away with the doodling and reatin less than I would normally.