I'm not buying it either.
On the map SteveS posted, note that two seismometers will yield two solutions. The other location is the blue circle in Indonesia. A third station is needed to pin down which of the two solutions is the correct one. Or a deduction from known seismicity. No information is provided as to the depth of the hypocenter. But again, more than two stations are need for that determination (picture those circles as spheres, and their resulting intersection pattern underground).
USGS doesn't show anything in the area, but they only show 2.5 and above.
And yes, I don't think there would be enough residual momentum once the aircraft came to rest on the sea floor. Hitting water is like hitting concrete at speed. A bullet only goes a few feet into water.