That's interesting. You said "small" cavities. It depends on how small they are. Some small cavities can be encouraged to heal themselves if they are not deep enough. I read this on the internet in a couple of places.
I would think a good dentist would be able to evaluate whether you would need a filling. I think it always pays to ask around, and get a number of different opinions. I was surprised when I recently learned that cavities can heal themselves, in some cases. I really had no idea. I used to think once you got a cavity, that was it. But apparently not.