Maybe he just started banging your wife

No joke. If you are married I would keep am eye out. Something else has either caused awkwardness or you do something to piss him off...

You shouldn’t have been late to the restaurant!

call the labor board, you can look up the number on google.
youll get your job back ,some money, or he'll lose his job. Either way it works out for you... unless you were working under the table

Family can't do that to you. I'd keep going to work. Fire at will is such bs
I would claim it's due to something like racism, sexism, homophobia, etc. Anything that is NOT covered by at will. Something you can challenge in court.
When someone fires you with a non valid reason or answer, fight it. That's your livelihood.

That is 1. Horribly illegal 2. Even if he was fired for any of the reasons you suggest he would need some kind of record either paper, email or video that was the case. 3. Lying in court is a crime and wuld not go well with out something to back up his claims. Filing a lawsuit can be exspensive doing so without a job bad filing a false claim is insan.

Something else happened, OP. You just don't know what it is yet.