No it's not. If they explicitly say they won't train on your data and then they do, it's going to come out in discovery of one of the lawsuits they're fighting, and the consequences would be significant. Plus there's little incentive for them to lie about it, given most people leave history on.
yeah because no large tech company has ever lied to their customers about how their data is being handled. oh wait there are lawsuits surrounding this sort of thing all the time.
I wouldn't trust them with nuclear secrets, but to say it's "insane" to trust that they're going to do what they explicitly say they're going to do just isn't logical.