Do you mean why would it be the case that a strong claim needs citation? Because it's a strong claim with no evidence (they provided some in another comment, sample size of 5...).
If you mean the claim itself, the person you responded to did not make it.
The sample is biased and intentionally so, the prior probabilities are pulled from general population statistics. Consider the likelihood of an event that should only occur 1/10K times happening 5 times in a row due to random chance, it is incredibly small.
If you mean the claim itself, the person you responded to did not make it.