I don't think you can say definitively it doesn't belong to him. There is a legal maxim that says the person who found an item has a greater legal claim to an item then any person other than the original owner. Hypothetically the original owner could have been anybody.

This would be more relevant if we were talking about a $1 chip. Casinos pay a lot closer attention to $25K chips.

THis could be regarded as salvage, since the casino is a 'riverboat' there may be applicable salvage laws in effect (maritime law is not me area).

I do think the casino may refuse to cash large denomination chips, where there is no evidence that a person has played that level and had access to those chips. But chips found may vey well be regarded as found property without an intrinsic value.

If the chips were 'found' in the casino, or in the immediate vicinity (or in the cage), or were in an enclosure which clearly identified the owner (money bag or lock box), or were taken from an area that was legally closed (ie much of New Orleans). The actual owner hen could meke a claim, and the possessor may be in violation of relevant statutes.

My only interest would be as a collector of chips, not as an actual instrument with intrinsic value. A $28k price tag clearly suggests (at least to me) a belief that these chips could be cashed in. And it is very possible that the attempt to cash them in could have negative ramifications.

I'm not sure how well I have answered your question, but those are my thoughts on the subject.