During war, we are gonna restrict access over large areas of water. And when we fail to identify a sub-surface threat as our own within the confines of that region, which will be public knowledge, we are gonna blow it right up. It's an us or them situation, doesn't matter if them includes neutral parties, they are not supposed to be there.
The S stands for Supersonic, so definitely below mach 5.
So it does - however SMART does appear to have a lot in common with Shaurya/K15. Similar diameter, similar fin placement etc which one can infer may also include a similar solid motor.
In this piece overt defense explores India's growing series of SLBM's and their derivatives including the Kalam series and SMART
It's possible it says Supersonic because the missile would decelerate to supersonic velocities before releasing its torpedo.