Most of my advisors are like that. In fact, that's the reason why I chose to work with them.
I agree with koolherc. You should be candid in everything you do; otherwise, you're jeoperdizing your credibility. You should ask about the things that you don't understand, but at least make an effort before you do so; make it sound like you did your homework. Even if the questions you're asking are trivial, doing that will show your work ethics. It will also show him how you approach problems. These things matter in the LOR; it's not just about getting an A+ in his course.
If you're professor is as smart as you say, then he can surely gauge your progress (btw, very few professors are not smart, period). And don't sweat over the pace of things, he knows you're a student and how research works. With that said, you wouldn't want to linger on one of your research assignments for an inordinate amount of time.