It is impossible to think of all the possible interpretations - I immediately went from G-Men = Gay men! Thinking you were making a joke. (about what G-men might mean - since it is a pretty aniquated term and not used very much except in very old movies.)
Well, I don't know why anyone would assume ALL or most FBI would be Gay because of JEH - Both Gays and Straights (homophobic or not) agree that Gays are a small percentage of total population.
I think the knee jerk part is what I already said Gay = Bad, and we (the FBI) venerate Hoover for being a really cool guy who made the FBI sophisticated and gee, a Gay guy couldn't possibly have done this AND as a straight person, I really don't want to contemplate that someone this smart and who was a lot of people's boss in the past, could be Gay.
Then again, you could be right or we both could be. Since people seldom tell the whole truth in polls like this, we may never know.