The requirement is that the AC ground, green wire, is to be tied to the DC negative buss on-board the boat and also go back though the shore power cable, two paths to earth.

You said "The AC ground should never be tied to the DC ground - the AC ground should only be tied to the ground through the shore power cord."

ABYC E-11

11.5.2.7.1. If an alternating current (AC) system is installed, the main AC system grounding bus shall be connected to

11.5.2.7.1.1. the engine negative terminal or the DC main negative bus on grounded DC systems, or

11.5.2.7.1.2. the boat’s DC grounding bus in installations using ungrounded DC electrical systems.

The ABYC requirement is that the green wire is connected to the ships DC ground or ground buss..