The numbers in Japan are most likely severely underreported. It's extremely hard to get tested. You pretty much need to have been in contact with someone confirmed infected or hospitalized to get a test. It's a catch-22.
With that said, I absolutely think the mask culture in Japan has dampened the surge a lot. In countries without this people just do the bare minimum to be compliant, so we have all these chin-wearers and nose-flashers. We're simply hopeless at wearing masks even with the strictest of mask mandates. So even if masks could reduce the spread significantly we're not likely to see the effect of that here.
>Japan which had a strong culture of wearing masks
Which is only sorta true in the sense that people who are sick often wear them and they're not almost unheard of like in the West. But pre-pandemic, go out on a crowded street in Tokyo and you probably wouldn't see more than a few masks if you saw any.
But even with the confirmed cases the trend in Japan is worrying, especially compared to other countries in Asia. They're setting new records every day: https://www3.nhk.or.jp/nhkworld/en/news/20201201_36/
With that said, I absolutely think the mask culture in Japan has dampened the surge a lot. In countries without this people just do the bare minimum to be compliant, so we have all these chin-wearers and nose-flashers. We're simply hopeless at wearing masks even with the strictest of mask mandates. So even if masks could reduce the spread significantly we're not likely to see the effect of that here.