What law would that be?
from the owner of a property to his listing agent is at best a breath away from telling the agent he won't sell his property to a Jew. Like refusing to sell to a black, or Catholic or Muslim. That's not lawful. In private the agent could pass it off, even follow his directions with a wink and a nod, but by saying it in front of a potential buyer he put his agent in a very difficult position as well.
He acted like a jerk, he apoligized, that should be the end of it, attacking the unknown butt of his joke aka the victim is inappropriate.