Anybody can make an honest mistake.
The question is, did he know that wasn't possible when he said it?
I'm no businessman or politician or economist, and I'm no oil or steel man. But even I knew it couldn't possibly be true. I don't know if there are any American companies sufficiently geared up right now to help him achieve that promise, we don't "do" much steel any more. And even if there are, can they do it cheaper than foreign competition?
He, of all people, should have known that. And my guess is he probably did, and lied anyway.