Asian airlines tend to be a bit more stricter and "by the book" when it comes to traversing into F territory if you're not actually seated there. They may accommodate you for a short visit to see someone but that's about it. I once unwittingly wandered into F from J on an EY flight after waking from deep slumber on an overnight JFK-AUH flight and used the toilet, not realizing that this was only for F pax use. Once I got out the flight attendant told me off and requested I only use the toilets for J.
On AA I was in J and my friend was in F (NRT-DFW), they had no problems for me to come and visit him (once he gave permission of course) and sat there for 2 hours chatting, and even poured me wine from F. I guess each airline has it's own policies of how lenient they may be on these matters but by and large the Asian airlines enforce their policy quite strictly.