Anyone who doesn’t like what someone does can call it robbery. Like charging a price that is too high in someone’s opinion.
But robbery in a legal sense is about property. If you dig up body in a legal cemetary, which generally means owned by some organization that runs the cemetery, that is probably real persecutable grave robbery. Elsewhere, not so much.
Assuming they mean this as a joke, there’s not really much point in responding at all. Bad jokes are best just ignored.