If his misstatements were mere hyperbole, the way a lot of Trump's are, passion might be a reasonable explanation. If not, then they are either lies (if Walz knew the truth and said something else), or bulls**t, in the technical sense provided by Harry G. Frankfurt: saying whatever is expedient without regard to its truth or falsity. (Incidentally, Frankfurt concludes bulls**tting is a worse enemy of truth than lying. The liar at least has enough regard for the truth to know it, though he says the opposite, while the bulls**tter has no regard for the truth at all.)