Again, what basis is there for him being gay other than “he is an asshole and conservative assholes are often secretly gay”? Which is “he is gay because he is an asshole”

The statement was made not because he’s being an asshole in general. It was because he’s being an asshole specifically targeting gays having equal rights. He could simply be a heterosexual asshole, but it’s not implausible that he has homosexual arousal and he expresses that with vocal homophobia (which would likely be due to his religion saying those impulses are sinful). There have even been studies on the phenomenon, such as here, which states:

Only the homophobic men showed an increase in penile erection to male homosexual stimuli. The groups did not differ in aggression. Homophobia is apparently associated with homosexual arousal that the homophobic individual is either unaware of or denies.

So it’s quite reasonable to take the research data that affirms the phenomenon and apply it individuals we see being very outwardly homophobic and presume that those individuals may be secretly gay.

Also, as mentioned: Plenty of gay folk are still afraid to “come out” because of bigots like johnson.

Absolutely. That’s why I will always vote against candidates who espouse such bigoted rhetoric.

But that wouldn’t be as “insulting” as calling him gay. So no, the focus is not on “secretly”

So is this also an insult to them for having “secrets” or whatever nonsense you are using because you can’t stop calling people “gay” as an insult?

Johnson, and other conservatives, would perceive “secretly gay” as an insult, but advocates for equal rights should not, because there’s nothing shameful about one’s place on the spectrum (assuming all parties are consenting adults). I did not perceive the comment to be insulting Johnson with an accusation, but rather asserting a potential context for his homophobic rhetoric and legislative agenda, and thus a reason to vote him out.