Close.
ARP responses from the firewalls are always CARP VIP ISAT CARP MAC. But those reponses are sourced from the interface MAC address, not the CARP MAC. The CARP MAC address is included in the ARP ISAT response, not the frame itself.
What steers the traffic to the proper node that holds the CARP MASTER is the fact that the CARP advertisements are sourced from the CARP MAC address. This tells the switching layer what port to send the traffic to. No traffic ever gets sourced from the CARP MAC at layer 2 other than the CARP advertisements.
This is why most CARP problems come down to switching, not pfSense itself.