he probably used the same username as something else and they were able to find you with that.
Its how people use IP addresses to troll people. Use their gamertag to find another social media profile then say "YOU'RE JOHN FROM FLORIDA RIGHT!?!?"
The night brims with defiled scum,and is permeated by their rotten stench.
Just think. Now you're all set to hunt and kill to your heart's content.