IAD (Washington Dulles) has these gates. You scan your boarding pass inside the terminal, as with any normal airport gate, but when you walk toward the tarmac, an employee checks your boarding pass a second time, and directs you to your A-B-C-D section.

One I tried to walk directly to my section, because the employee was chitchatting with her coworker. The employee grabbed me by my arm, with rather strong force, and demanded to see my boarding pass. I thought that was extremely inappropriate.

The comments you heard were inappropriate. They would be, regardless of race -- I'm also Asian, for what that's worth -- just saying that "Can you read?" is a rather common schoolyard insult.