Firstly, the colour of someones socks does not define their sexuality.
Secondly, you can just ask something on the lines of ‘do you even play badminton with your gf?’ This way you will know if he’s in a relationship, and if he’s gay, he’ll probably correct you. From what you said, he just sounds friendly and he hasn’t said anything flirtatious. He most likely is just trying to make a new friend soon as though you play the same sport. He also May fancy you, but tbh i think you’re reading too much into nothing. No one on here can clear this up for you so you’ll have to suck it up and just ask.