This isn't worth getting into a pissing contest over.
What I honestly think happen is that Walmart doesn't care all that much about proper ammo storage. It probably got a little condensation on it from temp changes, maybe from the cold truck to the warm store, or something similar. The water caused a little discoloration as it would on any copper or brass. The ammo is fine and the OP said he's already shot it without any issues.....let's move along.