Most of the time, they just get picked up as the go-to lingo from pugs. Theres not too much to think of it. People just call things what they roughly looked like/what was easy to call.
The only one with a story to tell is maybe haunter on badlands. http://etf2l.org/forum/user/77/ he used to be a roamer for TCM back in the day. He would always jump from that spot when people pushed in from choke and it got common for people to say, watch out for haunter which basically turned into, watch out for that spot haunter usually jumps from