The only interface that should respond to ARP is the interface that holds that MAC address.
If the Comcast device is also responding, it is broken.
This should NOT be the end of the world if everything it does is perfect from a CARP perspective but I suspect it is not.
The ONLY frames that should ever be sourced from a CARP MAC address (like 00:00:5E:00:01:0xVHID) Is the CARP advertisement itself from the current MASTER node. No other traffic should ever be sourced from that MAC address.
ARP responses for the WHO HAS the CARP VIP will be sourced from the interface MAC address and contain 00:00:5E:00:01:0xVHID in the ARP protocol payload in IS AT. What you are posting does not provide enough information because both the ARP payload and the source/dest MAC addresses of the frames themselves all matter here.
All of this pretty much has to work perfectly. This would not be the first time an ISP device was not compatible with CARP/HA because of games it wants to play.