It's call being a Chimera. It's when a child will have a completely different DNA sequence then one or both of their parents due to a genetic mutation. It's extremely, extremely rare and in some cases a person will have a different DNA sequences found in different parts of their body. I think there has been less then 10 reported cases ever. I can't remember where I learned that though, Google will probably have something about it.
And this guy is just an idiot who has no idea about the basic understanding of biology and pregnancy. Exoctic genetic mutations not counting.