That has not been proven. Do a little research on touch and transfer DNA.
This witness does briefly talk about that...
He basically says how the DNA gets there depends on a lot of factors. Finding DNA just tells us that it's there, it doesn't tell us how it got there. He actually uses the example "if I shake your hand, and then touch this counter, your DNA will be on the counter now".
I bet the defense was happy to hear that example LOL