By having test subjects, some gay, some straight, study a series of shapes and patterns, the researchers found that gay folks pay more attention to detail. Thus, they might be able to pick up small cues about a person's sexuality.
Which, honestly, seems like a bit of a stretch. Maybe gay people just don't focus on the big picture because it can be somewhat depressing, you know like socially and politically? We're not sure that it's a completely direct correlation between that and keen homo detecting. Though, a highly tuned sense of small details would be absolutely necessary for properly functioning gaydar in the Netherlands, where it is famously difficult to figure out who is gay and who is just Dutch. We would fail that test.