This is the first I have heard of a coach suing to get credit for a stroke improvement. What is the purpose of the lawsuit? To gain noteriety for yourself and to "prove" to the public you are an elite coach? Pretty pathetic...
Lots of pros show improvement in a stroke or fitness or some other aspect of their game over the course of their careers. Whether they choose to give public credit to a specific person is their personal choice. Whether or not this coach actually helped him is all in Nadal's perception. If Nadal thinks this guy wasted his time and says so pubically, then it doesn't matter what this guy claims.