He looks, to me, like a poorly bred Holland (or Dwarf) Lop. That's not meant to be an insult, but he just doesn't have the characteristics of a rabbit that was the result of a show breeding program. Know what I mean? He is still a very handsome little guy and looks like a very sweet pet bunny!
Hollands can be up around 5 lbs. if they do not inherit the dwarfing gene. If they do, they're right around 2-4 lbs.
Also, just a little tidbit- Black Tortoise (or "tort") is one of the most common colors in Holland (or Dwarf) Lops. So that is a huge indicator to me that that's what he is, or at the very least, a mix of it. Mini Lops do not generally come in that color.