Limes?

About three years ago I bought a small tree from a specialist citrus grower who had a stall at our annual Spring market. I was assured it was a lime.

Imagine my surprise when the first fruits came a couple of years later. Bright orange, rather small (pictured next to a normal mandarin from pal Teddy's tree.) and utterly unlike any other orange I've tasted - more bergamot and lime like. Not sweet, but not over acidic either. They may be uncharacteristically small as we have a very large mumber of fruits on a very small tree.

Might they be a Rangpur lime? Any other ideas?