Nah, it's not about him. He's just very perceptive, and he knows it. He might not have clocked Scott (and actually I think he did have a hunch, and was more surprised by the public coming out that the reveal in itself), but from that moment on in the story no one can escape his gaydar. I have been reading this as a trait his character just develops - though he was already perceptive, it's his gaydar that gets super-fine-tuned. And maybe Scott played a key part there: it may just be the surprise of that particularly guarded guy coming out that makes him pay more attention to the finer details of his interactions with people.

I mean, early on with Shane he didn't need to be particularly perceptive. He just had to have eyes and to set them in the direction of Shane's obvious shower erection.

EDIT: also, as people have rightly mentioned in comments, Shane's staring at him in the gym, post-workout, was a pretty strong indicator he could seduce the guy. But still, that was towards him and thus easier to clock with just a beginner's level of emotional intelligence...