The aural warning was "sink rate", which occurred twice (from NTSB brief). We can assume they were coming down at more than 1000'/min for that to happen. (a 3.25 deg CDA at 140ish kts would give a 800 fpm). "Terrain, Terrain" would be the proper warning for excessive closure rate ie RadAlt.
PEI, "Don't Sink" warning are on take-off and go-around only.
I wish the NTSB had provided the vertical mode in use.