Retire with 15 properties on 15 year mortgages

[Sovat C.]

I heard this on a pod cast before where the investor buys 15 rentals, 1 every year for 15 years.  He puts them all on 15 yr mortgages. After the 15th home purchase, the 1st home purchase should be paid off and he refinances and uses the cash to live for the year tax free.  The next year he would do the same on the 2nd home and continue to do so on the 3rd through 15th and it would repeat back to home #1 after the 15th home.  GENIUS!! Question is, how is he able to qualify for a mortgage if he makes no income?!?