Even if most people there support gay rights, many men can still be closeted.
Can you offer specific issues with that survey? The general "i think there are probably more closeted gay men out there' we can dispense with as that's a non-falsifiable statement.
I specifically picked Netherlands as they are as liberal a society you can have with regards to gay lifestyle as you will find on this planet, the survey was done online and had a large sample size (30k people).
Plenty of reason not to volunteer information about yourself even in the most liberal of societies.