actually, if this is your first annual extension from a 3 month Non O to a year, in my experience recently the 90 day requirement kicks in 90 days after the renewal date, as confirmed by the note stapled inside my passport
Im just about to do my first after being in Hua Hin for over 6 months on tourist/Non O visas as a result.
thats wrong. Its almost always the airline that takes resoonsibility for not accepting passengers with no onward ticket- not immigration. He wouldnt even have gotten on the plane to reach immigration.