1) It is the CTO who had not thought of the growth idea, not the person in charge of sales/marketing/growth. So it might not have been so novel after all had OP been talking to the people who really would have used it. Likewise, because it was a non-technical topic, it may not have been relevant to what the actual role being hired for was. Would you hire an engineer based on a good idea completely unrelated to their potential role?
2) It is possible that the company did not intend to steal an idea but were handed one anyway. Based on the post, we don't even know if the interviewer asked for the idea, or if OP volunteered it. What are they supposed to do? Are they expected to say, "Well, we have this great idea in front of us that can triple our growth, and yes it came about through a valid internal process, but not the marketing team, so we should not use it."
3) Unless the interview put OP and the company on bad terms somehow, there is nothing stopping them from dropping the CTO a line and saying - "Looks familiar - did some of that come from our conversation?" and see where that goes.
So yes, some type of recognition might be appropriate if it was a novel idea that truly came from this specific interview, but we have no way of knowing whether or not that is true, at least not unless OP tells us more.