I do not know whether they got a PWS caution, or warning.
The AFDS will respond to application of the TOGA pitch (two pushes on the go buttons) mode by commanding "the
lower of 15 deg nose up, or 1 degree below the PLI*", and maximum volume on the noise makers.
(I am sure I have seen more than 15 nose up in the sim in this type of situation)
i.e. at an absolute maximum, the FD/AFDS/AP or whatever manner you choose to perform the move, should not result in more than 15 deg nose up.
The -400 doesnt have any mode for this situation other than TOGA mode. <Well none that we are told about in the somewhat limited manuals.>
Where I am going with this is that max noise TOGA in a light a/c with no apparent windshear should have you sweating about getting the flaps up quick enough when you decide you've had enough... NOT hovering over the stall. Which in turn leads us back to your point alf... Why didn't anyone respond to the AP situation? Had that been reacted to, then the speed/pitch/navigation/altitude issues would likely not occurred.
*PLI is a PFD representation of the pitch attitude where the stick shaker will occur.