Most of the illegal/undocumented enter the country with different means. Latinos cross the borders while asian's used to board planes. Back in the 70's and 80's there were fake visa stamps but real good ones. Immigration was not that well equipped nor they knew anything about it. Late 80's and 90's, PC came along. PC stands for Picture Change. People with US visas would sell their passports for a handsome amount. Later they would report it lost or stolen. Experts forgers would pull the original passport holders picture out and an another person would use that passport with their picture.
So in this young mans case, his mom probably bought a passport, got the picture changed and brought him over here. Now did his mom commit a fraud, yes she did just like the so called 12 to 18 million living here is US.
Now I don't think the OP want's to hide the facts except he is shy about it. Remember one thing OP, never hide anything from your lawyer or you doctor. You have a wonderful opportunity due to this community to save thousands of dollars and also to get the job done.
P.S., this the most interesting post I've ever come across!