There is one study from a Denver emergency room - 269 persons and no data on whether "orientation" was self-reported or not.
Finally there is one study cited where persons who self-reported their own orientation were shown or listened to child porn. People who volunteer to participate in sex surveys, especially ones with such a disturbing premise, are an extremely skewed group to begin with.
He admits that both the latter (possibly due to their highly self-selecting nature) are unable to establish his position "scientifically". Therefore he is clearly depending on the first study as his proof. It comes down to one study with a sample size of 175.