A Thor style pure kinetic weapon was supposed to impact at around Mach 10, but this is a scram jet and as such should be able to maintain a significantly higher speed. Granted it's unlikely to maintain that at sea level, but it sounds like it impacted the water reasonably intact and so could probably do a powered dive. Also, around mach 9 is the break-even point where high explosives have more kinetic energy than chemical energy so even if it hit's at say mach 12 that's still a lot of energy.