Is it true that was the best sex they ever had? Your guess is as good as mine.
If they were experts on getting sex from hookers, and they went to Filipina hookers, then that would make them far more expert on hookers than most people.
However, I find it particularly odd that any part of what you heard would make you think that it has the ring of any sort of truth?
The people that passed this sort of opinions on to you were military who had most likely a lot of spending money...tossed it around while alcohol impaired. Just what sort of women would these men be running into? They sure as hell weren't seeing a fair cross-section of Philippine's finest citizens, would you think?
As a man who was brought up in North America, I'm not only not an expert on that subject, I think anyone who thought Philippines culture encouraged their women and girls to be sluts to be pretty biased and cotton headed.