Lidl & Ornamental Citrus Trees - non-edible?

Was wandering around the corner-shop Lidl yesterday and stumbled across some citrus trees for £20, with Kunquat and Lemon varieties, at least.

Looking on the care-label there was a big "X" through a piccy of a knife and fork, which logic suggests means "don't eat".

What gives?, are there inedible varieties of lemons?

I expect they were developed as lookers not eaters so Lidl are just covering themselves in case people complain about the edibility of the fruit.

Just bought some South African Southern Belle plums at the Co-op, big fleshy plums with tiny stones they look good but are inedible.
Selective development gone pants.