Actually it looks like a friend of Borras's made the video:
Durante la sesión de trabajo con Nadal, un amigo de Borrás grabó la sesión en vídeo para poder corregir los defectos en el saque.
(During the practice session with Nadal, a friend of Borras's recorded the session on video in order to correct the problems with Nadal's serve.)
That's from this article, which also mentions Christophe's video:
In that article, Borras claims that although he and Nadal only worked together for two hours, that session was a turning point in Nadal's serve.
If I understand this part right, he also says that he wasn't compensated for this session, because it was a trial lesson and the Nadal camp didn't follow up:
"No se me abonó cantidad como prestación por ese entrenamiento porque quedamos en que hablarían después conmigo para concretar si iba a seguir colaborando o no, y no lo hicieron", aclaró.
I can see why Borras might feel a bit ill-used, but claiming that a two-hour lesson in 2009 was a turning point for Nadal's serve seems like quite a stretch, and releasing a video which was ostensibly made for training purposes as 'evidence' doesn't seem very professional.