Everywhere I walked in Poipet I heard the cry of "HELLO!!!". People of all shapes and sizes, children, teenagers, middle aged and even some old people said "HELLO!!!" to me as I walked past. The kids did it most often and were very happy when I replied with my own "Hello".
I had heard the hello stuff quite often in Thailand but that was mostly from children, in Cambodia there were no age barriers, everyone yelled it out, sometimes 2 or 3 at a time.