I don't get it. I'm not sure that it has anything to do with tipping.

Does it make you feel better really? Imagine the situation is reversed. You're first or second in line at a cab station (and you tip well in the first place; let's just assume). Suddenly, a cab appears and rather than picking you up (as expected being the first in line), he picked a foreigner that's third in line. I don't imagine you would be happy. That's why there's a line. That's why you're waiting there.

It's more or less a kind of 'profiling' that happened. In my mind, it has nothing to do with "proper use of taxi driver tip" because he does not know how you will tip in advance.

(By the way, I have seen two young ladies throwing a tantrum at the cab service rep manning the line in Ft Lauderdale (cruise) because they were in a hurry, and wanted to cut in line. The cab were able to keep them in their place for a while (explaining that others are waiting) though they were able to get their way, much to the disgust of other people who witnessed the episode.). Not your situation, clearly, but something I just remembered.