People, people, people.

"Substance over form."

Repeat it three times and it's yours.

We don't really have enough facts and circumstances, so no one should jump to conclusions.

But sometimes, the name on the deed is not the owner of the house. 

Occasionally the name on the 1099-S is not the actual seller.

Why didn't the son just deed the house back to Mom, before the deal closed?  (Well, OK, people who practice hillbilly probate aren't always the brightest bulbs.)  Or maybe the son is in a 0% bracket, and Mom is at 30% with state taxes and also looking at higher Medicare premiums.  Does that change your answer?