That’s definitely one signal, but it can be refined by tracking whether the search led to click-throughs, conversions, a different search, a bounce, etc... The conversion is the most important event, but there are a lot of important features aside from that which we'll use to improve results over time.
If you're interested, our behavioral api (https://constructor.io/docs/#behavioral-data) goes through some of this as well. We've done a lot of work to figure out which signals are the most important, and are continuing to develop this feature all the time as we acquire more data.