Hi, if you look at the thread there is this message at the top which is american airlines policy -
On Flight operating domestically and on flights departing from the U.S., customers may use the lavatory in any cabin.

On International flights returning to the U.S. from non-U.S. locations, the Transportation Security Administration (TSA) requires airlines to direct customers to use lavatories in their ticketed class of service. This directive applies to the use of lavatories only and is not meant to restrict the movement of passengers between cabins for other reasons (families/coworkers).

If I was an AA economy flyer and was allowed to use the J loos on the flight going from the USA, I might well believe I was entitled to use it on the way back as well - regardless of announcements.