Why is my male friend mad at me?

So a friend of mine and I play games together and he told me which country he chose and the country his brother chose, normally I happen to choose ones next to him by coincidence. This time I took one next to his brother and further from him. I took North Brazil while he took South Brazil. When I told him, he messaged with just "okay" (He usually adds smiley face) Then the next day I messaged him and he messaged me back a day later with also a pretty cold attitude and didn't reply when I answered him. I think he's mad, but why is he mad?
Why is my male friend mad at me?
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