Ports using UDP

I did a test using Ethereal to try and get an idea how when using P2P ?Bitcomet? the ports are used or allocated. This is how it looked.

UDP
Source port: 24142, Destination port : 17592
24142 13488
24142 18311
24142 27034

So it looks like the Source Port being my PC and the Destination being the other side. I would imagine that the destination is changing because I am connection to a number of different users? I am a bit unclear on this I must admit.I would have thought it would be determined by what you are doing that would allocate what port you connect to. Why would it change from PC to PC if my theory is correct that I am connecting to different PC?s