1. The video has not been confirmed by CNN or any international source.
2. The sub was in international waters.
3. if India had actually intended to launch an attack it would have brought more than one sub. Pakistan does have anti ship capabilities, so the Indian Navies best strategy would be to overwhelm the PN through sheer numbers.
My guess is that it was probably scouting and testing Pakistan's reaction. Or potentially even trying to instigate Pakistan into attacking first, although that is more unlikely.
Also the video has not been confirmed by international sources yet
@waz @Dubious @Oscar