My friends guy friend thinks he's the father to her 4 year old child

Why would he want the responsibility of a damned kid that isn't even his?

None of this is normal.

Sounds like your friend might need to take legal action against this guy. He might crack it one night and steal the kid or something.

A guy wanting the dna test to come back positive. Now I’ve heard everything

Sounds like you need to pull up the office tv show paternity test clip.

The only thing connecting Michael to the baby is delusion.

"he's even saying he has 2 different DNA strands"

Weird as it sounds, this is possible. Chimerism is a condition where an organism has more than one set of DNA in its tissues. So it is possible for the DNA in a cheek swab to be different to the DNA in a guy's sperm or a woman's ova. It used to be thought that this was incredibly rare and not many cases have been confirmed, but apparently some geneticists now believe that up to 10% of the population could be chimeras, although the different DNA can occur in any organ, not just the testes and ovaries.

There have been a few paternity cases that have hit the news where a parent has been found to be a chimera, including a very strange one where a woman tested as not being the genetic mother of a child, even though she'd got pregnant in the normal way and there was no question of baby-shuffling in the hospital or anything like that. Genetically, she was the child's aunt, since her ovaries had started out in the fetal tissue of her twin, but during the development of the fetuses, she'd absorbed her twin and the ovaries moved over to her fetus. The so-called "vanishing twin" phenomenon apparently isn't that uncommon, and a good many pregnancies start out as twins, but only one survives beyond week twelve.

As you've told the guy, this is not something he can self-diagnose and reasonably claim on the basis of nothing more than his gut feeling. However, it would be pretty simple for him to get confirmation if he wished to: all he'd need to do would be to submit two samples from himself for DNA testing, the normal one from his cheek, and another swab that he'd swirled around in his semen.

I'm not clear what the guy means when he says that the mother somehow cheated on the DNA test. If it was a home-test thing, then obviously the mother could have taken a cheek swab from whoever and claimed it was from the baby, but if the sampling was done by a third party, his claims don't sound rational.

In fact, from how you describe his behaviour, little sounds rational. Assuming the worst of him, it could be that he's trying to use the child as a means to impose himself on the woman and force her into some sort of relationship with him. I suppose there's some small chance that he's just very keen to have some sort of a relationship with the child - a few guys do have strong paternal urges - but from how you describe his actions, it really doesn't sound like his motivations are that positive.

Poor dude.