Cukor did absolutely nothing wrong.

The building has a security system. The front door locks automatically, and non tenants who wish to enter the building, must use the intercom system to contact the tenant they wish to see, and be buzzed in.

Michel refused to do this, and attempted to bypass the security system that by entering through the door before it closed in Cukor's wake. This practice is known as tailgating. And for obvious reasons, it's not allowed.

Michel should have waited outside, used the intercom to call the tenant and wait to be buzzed in. He doesn't get to bypass the security system by taking advantage of Cukor's exit.

I would not expect you to let someone you didn't know to enter your building by bypassing the building's security system. And I would not fault you for acting as Cukor did. Race is completely irrelevant to this question and Michel is 100% in the wrong.