A lot of guess work going on with regards to how cabin might be warmed with excess heat during the pre-conditioning when using charge and depart.
the discussion regarding use of coolant to heat the cabin, would be during the pre-conditioning phase using the charge and depart setting..... a resistive heater warms the coolant, which circulates around the battery and then through a cabin heat exchanger, where if any heat is left over after warming the battery is available to the cabin.
Since a 120V EVSE can only give you 1.3kW and even a 240V EVSE can only give 2.6kW at 12 A, (or even 3.3kW if supported by the EVSE and the BMS is set accordingly) a 5kW element would need to steal from the HV system during the 30 minute pre-conditioning which would be counter productive to the range maximization intention going on at that time.
I suspect that the cabin heat uses both the coolant and a PTC in a cabin heat exchanger when driving, but only the coolant that has been heated to warm the battery when pre-conditioning is going on.