Mini-Rex rabbits tend to have short, curly whiskers. From what I can see in the picture, Cinnabun has long, straight whiskers. Also, the very definition of Rex fur is that the guard hairs and undercoat are the same length, so the fur stands up like velvet. From the picture, it seems like there are lots of longer white guard hairs over the shorter black fur, which doesn't look like Rex fur to me.
MR mix is still a possibility - nearly anything is a possibility - but I don't see enough Rex-like characteristics to think that Rex is a big part of the mix.
Personally, I'd settle for "cute bunny" as a description.