If it’s meat, looks like Rocky Mountain Oysters. Thought of this fine community the instant I saw it. Your guess is as good as mine. OP stated, ‘Good God !!! Please don’t tell me they’re some animal’s kidneys - that’s going too far , pizza explorers…… baaarf!!!’.
This is how I imagine pizza would look like in a city run by Tolkien Orcs.
Looks like meat’s off the menu boys, but we’ve got this suspicious looking pizza