“He should sue them.”
Chances are he signed an employment agreement when he was hired that dictates arbitration. If the arbitrator says the store has to rehire him, then they will make his job so difficult he’ll quit. Chances are good that he violated a clearly written policy and will lose arbitration.
The last two aerospace companies I worked for had a set of policy manuals that filled several large three ring binders. Everything you could think of and often things that were routinely done were against one policy or another. They could literally fire you for almost anything.
Nobody has time to read all that crap. People get fired for no good reason. Good news is that there are plenty of good jobs available.
When I worked at Lowe's, when they wanted to fire a person they reviewed the in store camera footage (going back many months) looking for that person committing a safety violation to use as a pretense for firing them.
Dooshes!