If he's asked her age before taking her to a party and having sex with her, then it indicates that depicted her make up and being out at 4am, but he still had enough doubt to ask her her age? Surely, if you have to check that that someone is 16, the safest thing to do, for hi and her, is not fuck them. Going without sex isn't a big deal.
Also, why does it seem to be mostly men who mistake underage girls for 16 year olds, women don't seem to be accidently having sex with underage boys in the same numbers.
My own 12 year old dd looks older than she is, males have thought she was over 16, without make up etc, (bus fares, trying to get her to sign up for charity donations etc) but no female has ever made the same mistake. Catcalling is similar, it was worse for me when I was 12-14 and people would defend men doing it by saying it's hard to tell a girls age, I don't think it's as hard as its made out to be tbh.
I wouldn't ask for ID if I thought the man I was about to have sex with was underage, I'd nit have sex with them full stop. But I don't see why asking to see ID just to make sure you're not about to rape a child is so outrageous. It's common for ID to be asked for to take part in age restricted activities, and it's common for underage people to lie about age to take part in said activities, like gambling, drinking, smoking, if you wouldn't serve alcohol to someone you had doubts about just based on their word, then maybe don't stick your dick in them either.