Protip for eating
PROTIP: Close your mouth while eating, you sound like a horse!
In China, eating with the mouth open is normal. (Are any other
countries like this?)
Me, my boss and a guy from Singapore office were the only non-Japanese in that room of 60+. All others were men on overseas assignment from Tokyo home office.
Same rules here as for other trading floors: lunch eaten at desk. At IBJ, a woman with a wheeled cart arrived at 11:30am daily, quickly traversing the aisles between the long rows of trade stations, collecting money, serving meals. Soon the raised-floor room was filled with the sound of noodle slurping, soup bowl draining, lip smacking and burping at will.
My co-workers were fastidiously polite and tidy, But their culture considered "silent eating" to be bad manners (was a sign that the food wasn't enjoyable or good). It is impossible to make that volume and variety of noise without some amount of open mouth activity.
So in answer to your question, "yes". In the U.S.A., I saw Japanese i-bankers eating with their mouths open, en masse, on a daily basis. It was very normal behavior at IBJ.