An exception to this that I wasn't aware of until just last month is the boarding platform for the bullet trains in some stations. I had to walk through a dense cloud of cigarette smoke on my way to my bullet train car at 9am on a Sunday. That was not pleasant.

From my understanding and observations when I visited Japan for a couple of weeks, Japanese people don't eat/drink/smoke while walking. Even for outside vendors, they will eat it on a nearby bench or stand and eat it before moving again.

I did see smokers often in the smoking areas. More than I see in NYC.