Well, he could have assumed she is paid for it and does it for money. I mean, I agree that remote island full of underage girls throwing themselves at old men raise questions and most reasonable men would conclude it's too likely to be coercion rather than voluntary sex work to get involved but I still think it's not ridiculous to have discussion about it. I also happen to agree with Stallman about the wording. If you call any activity that constitutes statutory rape in some jurisdictions a sexual assault you're doing disservice to people who experience what is more commonly understood as assault as that devalues the term and the suffering that comes from it.