I've seen airline employees at YYZ terminal 3 baggage claim belt only because YYZ T3 is an absolute mess for transfers and they're trying their best to help passengers' bags make it on to their flights. However, your case is a bit of an abuse of position. CBP officers are the only ones who should be directing people for inspection/security/whatever, not DL redcoats.

I've seen clear racial bias by DL employees. I posted a few instances within the past few months about how DL FAs abused an elderly lady and her daughter on DL159 or how people at the DL check-in desk tried to prevent certain people of a certain race from boarding their flight to AMS. The only thing that can be done in the future with these folks is to avoid them, deal with a different DL employee while keeping your cool, and then report them if it was a severe case of clear bias.