When you said that they decided to hire you, was that something they told you right after the interview? If so, I think it would've been prudent to follow up with both the CTO and the recruiter after a week or two had passed. Worst case you'll just look enthusiastic about your new job, and there's little harm in that. It's always possible for these sorts of little mishaps to happen, even if it weren't through a recruiter. A short email could've saved much confusion.