It's still an alternate universe, and in this one Sulu is gay.
Its a rewritten timeline, but the same physical people supposedly exist there. Quinto and Nimoy are supposed to be physically the same person, just having experienced different events. Its the same Sulu, whom Takei himself has always described as straight. Again, you have to resort to something like "which sperm made it" and a ton of butterfly effect "timing" issues in order to explain that this isn't the same exact Sulu. OR that experiences and surroundings attributed just as much as genetics, resulting in a different personality and preferences. I'd agree if it was a straight reboot, but its not. Its just not a clear cut answer, which could have been resolved with introducing some new characters.
Completely off topic, but I would have been much more okay with the reboots in general if they had just been straight reboots (and opening during the mission, like TOS did) - but they wanted to do this whole origin story thing with cadet Kirk. Shoehorning in the normal supporting cast was the biggest problem - they could have had a gay character right at the beginning with a clear slate and introduced Uhura, Chekov and Sulu later on in later movies. I hate Quinto as Spock, but would have loved him as Gary Mitchell, and there are so many characters between the 2 pilots that they could have gone in any direction with them - Kirk, Kelso, Mitchell, Finegan, etc at the Acaedmy, with Spock, Pike, Colt, Number One, and Jose etc on the Enterprise.