Odds of a person having a genetic mutation where they are immune to cholesterol when most people aren't: low
Odds of a person choosing to make a documentary: low
Odds of a person choosing to make a documentary about themselves going on an extremely high fat diet for 30 days: extremely low
Odds that this same person just happens to be one of these people who is genetically immune to cholesterol....... REALLY?
You have calculated the odds of any given individual creating a documentary about going on a high-fat diet and having a genetic mutation. However the claim you are trying to refute is that this particular individual has a genetic mutation. Since this particular individual is known to have made a documentary about themselves going on a high-fat diet, you must instead look at the conditional probability.
It is likely that making a documentary about going on a high-fat diet is totally uncorrelated with having a genetic mutation. This means that the probability of this person making a documentary about going on a high-fat diet is divided out of the final probability, which reduces simply to the probability that they have a genetic mutation.
Of course it could be possible that making such a documentary is negatively correlated with having a mutation, in which case your point stands. However I highly doubt this is the case.
However it could also be the case that making such a documentary is positively correlated with having a mutation, in which case your point is moot. It is more likely that this is the case, as this particular individual may have known beforehand that his body dealt well with fat; also, other individuals may have made a similar documentary but never published it because the outcome (getting fat) was as expected.