Ok, to play devil's advocate for a moment, he might be more or less done book 1 and Ina stage where he's waiting for feedback from whichever test audience and editors he's pulled together. This means he'd actually be in the right to be writing book 2, as many professional authors do just that to keep on schedule, there's no break while you wait, just the next book. There could also be details concerning publishing and manufacturing holding up book 1 and so he's dealing with that while he writes the next book and therefore can't yet give a release date.
However, we don't know what Sam is working on in terms of book 1, his lack of accurate communication on such is a determent to being able to feel like he's not just biting off more than he can chew.