The study hasn't concluded it is specific to Sanskrit. As it is difficult to obtain a sample close to the number resembling people chanting and memorising verses from such a young age for several hours a day.

Previous studies involving other brain activities have shown improvement in grey matter before, for e.g. London Taxi driver in one study showed improvement in brain development.

https://www.wired.com/2011/12/london-taxi-driver-memory/