Older systems including the older versions of Blue Cruise may not go around you, but you also don’t know if they even have radar cruise control enabled.
If it’s a simple enough system maybe it would just keep going the same speed no matter what until it hit you.
Blue Cruise, and I assume Tesla's FSD as well, will simply change the lane and go around you.
If the guy had a simple LKAS and adaptive cruise control on, then yes, you're right.