The good thing about this is that people maybe start questioning if a product for some reason gets “better” because their favorite actor says so - because he got money for doing so.
Imho, he doesn’t need to warn his fans, they are not affected by this at all. Maybe the toothpaste is even a bit cheaper compared to the one that actually paid a (probably very pricey) Hollywood star for their ad. He’s the victim, not his fans.