Free entry to Hong Kong

wow! i have just Learned that zambian passport holders have free entry days to HK not exceeding 90 days provided i have a return ticket and passport Thanx to Joey from the united kingdom. But there is a question behind this, remember that i will leave through HK to zambia and return back to china through HK, so my question is will this be allowed? i dont understand what you mean by return ticket, return ticket to Leave HK and back to original destination or return ticket from whereever to HK? my point is i will use HK as my Exit hub to leave mainland PRC going to zambia and again i wil use HK as my arriving destination as i will be on my way to mainland PRC for my school, is this Ok with the immigration? thank you.