I think he means with "closeted" TOS Sulu. TOS Sulu never showed interest in men, although there were a lot of hot ones his age on the ship, not to mention hot alien men. All the other characters showed obvious interest in the opposite gender. The other guys had all female love interests and the women had male ones. Only he didn't show in 102 episodes and 6 older movies any interest in other men. So why not? Now Takei thinks he didn't, because Sulu was in the closet. He thinks that making new movie Sulu gay means also, that TOS Sulu was gay. After all ST09 wasn't really a clear reboot. Sulu's sexuality shouldn't have been affected at all by Nero. Nero only destroyed the Kelvin before Sulu was grown up. So with other words Takei thinks it is canon now, that TOS Sulu is gay. TOS Sulu didn't express it though ever, so Takei concludes he must have been in the closet. And a guy feeling the need to be in the closet in the 23th century, is for Takei against Gene's vision. At least that is how I understood Takei's reasoning. Maybe he says more about it in the future and it will become clearer, what he means.
Even if you decide that TOS Sulu was gay just like nuSulu, it would still not make sense for him to be showing interest in other men. He's married and committed to his partner.