Woolf,
I suggest you read my post again.
The 155 level off is a baralt (ALT) capture predicated on the radalt, giving a nominal level off at 65 ft. If you level off and then the ground rises, you fly into the ground. It's not a foolproof system; it's a first line of defence against stupidity.
The CRHT is a preset value much like ALTA, selected by a rotary knob next to the HDG select knob on the APMS. The value is selected and displayed (as in the photo) but the mode is engaged by pushing the knob. It is always a collective coupled mode with a non-changeable vertical speed. It is easy to reach down and turn the CRHT knob instead of the HDG knob. The FLM forbids the use of this mode in IMC or over land, so it's hard to see why else it would be set at 490 ft (it's also in the previous photo at an earlier stage of the approach). The radalt reading comes in at DH plus 500 ft; we can't see the DH figure as it's masked behind the cyclic (below the radalt tape on the ND).
I agree it's probably a training flight, showing the level off function.
I assume you are on the 225 or L2
Cheers