My guess is it comes from either crates or mobs as other reversed foods. Might get 10-25k for it, but I don't think its worth anything more than that. Even if you can verify it no longer spawns, I don't think the desirability is there among collectors to qualify for a high price. Someone might be interested in it for decoration purposes as it might position differently than a normal one.
That's my opinion, but maybe someone has a different one or additional information. Best of luck with it!