It seems to me that it's clear he's not trying to claim that the character of Batman or of Bruce Wayne is of homosexual orientation. He's saying that the construction of the character has much in common with what otherwise might be seen as stereotypical (and rather outdated) traits of the homosexual man.
His life is built on a dual identity - one face for the daytime corporate business world, and another for the nighttime where he dresses up in weird outfits and prowls the streets looking for other unsavoury characters. He has an older mentor who he relies on to keep his secret. He has a younger protege who came from a similar difficult family background, and who he teaches in the ways of the night-people.
That's the kind of stuff Morrison is talking about, to my mind. Not saying that the character is an actual homosexual.
It's like Raj from the Big Bang Theory
. People say he's gay because he likes chick-flicks and pot pourri. Those are incidental things. Yes, he may be playing the "gay role" (again, defined in hugely and rather offensively stereotypical terms) but he is doing so while not being an actual homosexual.
That's the way comics were written back in the day, the way all sci-fi and fantasy works. You cloak the issue you actually want to address in tights and a cape, so that people are distracted by the outer covering while the internal issues creep in unnoticed. The X-Men
was a totally gay metaphor story decades before any actual homosexual character appeared in its pages.