Sharing political opinions? He could just be rude to someone who was gay. And then project his own rudeness onto his victim.
This actually happened in my workplace, I recognised a coworker as gay long before he told me, just from his vocabulary.
Also, wouldn't the taxi driver also have to know about these clues?
With all respect, I think the scenario "Taxi driver planted/used as an interview prescreen is openly anti-gay and sniffs them out." is a bit contrived.