This isn't a stupid question. The guy didn't know how much heat the CPU actually produced when not in heavy use.
Anyways, yes you will still need a fan and heatsink. It doesn't have to be a good one. This is because although the CPU is not being heavily used, it still is on, and as long as it is on, it will continue to produce heat, just not a lot. Enough to burn the CPU if left without a heatsink for too long.
Sorry to be curt, but it sounded like a joke. Nearly every processor since the original Pentium has required a heatsink.