They are talking about the airsoft ar lowers, some of them are made out of metal. The thought is you could disassemble the metal ar15 airsoft and rebuild an AR15 using only the airsoft lower.
That would require a little more than "Not a lot of work"
Besides....if you are going to build a gun why not build a better gun? Like a full auto suppressed zip gun (Could be built for under 50 at home depot.....or some I am told).