I had that same experience when returning from Hong Kong to Nigeria, i wonder whats wrong with our immigrations and customs all they are interested in is what you have in your luggage, not even your pocket, i hope someone reads this post and pass it on to those who needed to know.
First of all, once you get into Hong Kong or China, you will be conned to sell your passport and return ticket by the Nigerians over there telling you its useless after 3 weeks of stay according to your visa, thus it makes you lost the chance of ever coming to Nigeria LEGALLY.
then you proceed to UN office to stand as an asylum which will not even guarantee your stay in Hong Kong for more than 2 months, then you start with the going and coming for AC(asylum certificate) renewal, that itself is gonna wore you out, then you decide to just face any means possible to work and raise money (you only have a visitors visa NOT ALLOWED TO WORK)
so they ended up getting into drugs and other illegal stuffs, in my own case, i ended up as a teacher, saving and living on Filipino girls. When its time to go home, i BOUGHT A NIGERIAN PASSPORT(am dark skinned) THE GUY IN THE PASSPORT IS FAIR,,, i got home and i had no second checking by Nigerian immigrations........