He may have been applying SWAG principles to the Risk Factors and coming up with HPV as a most likely cause. That would be an estimate on surgeon's part, not the result of an actual test.

Problem is that there are likely risk factors that haven't yet been identified, just as HPV is a relatively recent contender compared to alcohol and tobacco.

Note that cancer risk factors contain most of the popular human vices like alcohol, tobacco and sex -- Seem like only drugs are missing!