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.
If the pain is lacking so is the discipline...
"the only 911 call I need is chambering a round" - Mr. Muller, MO car dealer