I mean, you're technically correct in the sense that "liberal" and "leftist" have been erroneously conflated in American politics for some time. So yes, a "liberal" not voting for Clinton would be out of character.

A leftist not voting for Clinton, however, seems perfectly reasonable, considering that she is not even remotely leftist. She's a neoliberal, who ran on a neoliberal platform - one that would've made no meaningful effort to advance actual leftism in this country. It would've been, at best, appeasement.