4 lbs rules out mini lop... it also rules out show quality (true dwarf) Holland Lops, which I imagine is why you're having trouble figuring out what he is. I'm 99% sure he's a FALSE dwarf Holland Lop.
The dwarf gene is a bit unique. One copy = "true dwarf" (as in dwarf sized) but 2 copies (one from each parent) = peanut, a non-viable offspring unfortunately destined to die before reaching weaning age. In a cross between two "true dwarf" parents, 50% of the offspring will be true dwarves (one copy of the gene), 25% will be false dwarves (no copies) and 25% will be peanuts. Most breeders cross a true dwarf with a false dwarf, generating 50% true dwarves, 50% false dwarves and 0% peanuts.
Like both Hollands I've had, I believe yours to be a false dwarf; they usually have an adult weight of 4-4.5 lbs.