He just changed his mind!
Seriously, this is one of my pet peeves–the conflation of the concepts of lying (make a statement one knows to be false about a present or past circumstance) and the breaking of a promise, or changing a position. They really are different things. I remember being particularly irritated during the impeachment saga when people said something like “So what if Clinton lied? Bush lied, too. He said he wouldn’t raise taxes, and then he did.”
Even leaving aside the fact that Clinton’s lies were under oath, there is a distinction between making false statements, and taking a course of action different than that previously proposed, or even promised. Sometimes circumstances change, or new facts come to bear, in which case it’s not reasonable to hold to a course just for the sake of being consistent with past statements. That doesn’t mean that changes of position shouldn’t be criticized–just that they shouldn’t be considered “lies.”
In the case at hand, of course, it does appear that Schwarzenneger was being untruthful before the show, but there’s no way to know that for sure. It’s at least conceivable (though not likely) that once he got up on stage, he decided at the last minute to go for it, so the headline, to me, is too strong.