Promissory estoppel has four requirements:

• The defendant made a clear and unambiguous promise.
• The plaintiff acted in reliance on the defendant’s promise.
• The plaintiff’s reliance was reasonable and foreseeable.
• The plaintiff suffered an injury due to reliance on the defendant’s promise.

Assuming purchasing a winning Powerball ticket meets the definition of a “promise,” I’d say the guy has a reasonable argument for points 2-4 but that Powerball also has an argument for (1): that with the winning numbers not being consistently reported, the “promise” was not unambiguous.