The context of the following conversation is Alex is a professional athlete.  He bet some strangers that he could win a race and won.:
Alex says I am so happy today..
The friend responds Anything exciting happening?.
Alex responds I bet some of them that I could beat them in a race..
The friend responds And you won?.
Alex responds I guess they didn't know I was an athlete. I won the race easily..
The friend responds I'm not surprised..