A dna test can be wrong. My husband had one come back 99.99% saying he was the father and we knew the baby wasn't his because the dates did not add up. He had a second test done which tested more markers and it came back saying he was not the father.
If the people who are testing the Dna and they do it by hair that means that they have to pic a peice of hair of that person and if that person was trying to be someone else they could pick a peice of hair off the person that they were trying to be.
The chances of a DNA test being incorrect are almost impossible if not totally impossible.