Just about any successful company or website will have a similar chart if you look for "X alternative" google trends, corresponding roughly to the company's overall popularity.
https://www.facebook.com/notes/mike-develin/debunking-prince...
You could argue "if people are searching for alternatives to my service, that means they (1) care enough about a core aspect of my service that they're inclined to find an alternative rather than simply leave, and (2) other alternatives/competitors are not already obvious (market dominance)."
Of course that's a stretch, and if enough people really are dissatisfied with your service you stand to lose them to alternatives, but I guess the point is that google trends doesn't really imply a whole lot in this case because it's going to be biased by many things - including overall popularity.