I don't believe this is relevant to ground-to-space communications. The way I read the article the laser pulse has a short range, ionising the water in the vicinity of the buoy, which creates sound waves which emanate out to wherever the sub is. The laser isn't bouncing back and forth from sub to buoy.

As the communication is via sound and not laser it also means that anyone else in the vicinity could intercept the message. Strong encryption and authentication would still be required.