They are just different ways of categorizing things in increasing level of detail. A boylover is a subcategory of pedophiles that includes only those whose attraction is towards boys and who have a romantic as well as a sexual interest. A pedophile is a broader category that includes many different kinds of individuals including boylovers, girl lovers, and child molesters.

It's no different from how we categorize any other thing. We can say a fox is an animal or we could say a fox is a mammal. Both of those are correct but one definition is more detailed than the other. All mammals are animals, but not all animals are mammals; some are reptiles, some are amphibians, some are insects, etc. By that same token, all boylovers are pedophiles, but not all pedophiles are boylovers.

They aren't two distinct categories that exist independently, one of them is a subset of the other.