The EGPWS mode that triggered the event was the terrain clearance floor or TCF. The SOP for this is select OFF the 'TERR' pb on the EGPWS panel on the overhead captain side. The requirements are that the approach is visual and in vmc.
The logic is that on some visual approaches, the terrain is not in the database and the computer reverts to a standard model that does not recognize special procedures pertinent to the specific visual approach at the particular location.
This is in the FCOM 1 in the NAV section.