I understand that masks and good hygiene are an important factor, but I don't think that's just what it takes to stop the spread of such a contagious virus.
I think the masks and hygiene are the most important factor when it comes to a coronavirus carrier spreading it to others, especially the ones with mild cases or are completely asymptomatic. Based off
this article, most infections are through non-airborne sources like mucus from sneezing or coughing, and the airborne variant is less common in real world scenarios, mainly limited to toilets and hospitals. There was a case of a coronavirus patient not spreading it to their household members, which wouldn't be possible if it was a primarily airborne infection. Having a mask means a carrier is significantly less likely to spread the non-airborne variant through their own coughs or sneezes since the mask catches most of it, and the masks worn by others will protect them. The good hygiene means any residue in public areas is properly dealt with.
Hokkaido was the place that was hit the hardest, and was properly locked down. The footage we see of people not social distancing aren't from that area, since it potentially hasn't spread that far, which is why people are mostly out and about in these places. If the populated areas have calls for a proper lockdown from the government, the citizens would do so, which is evidently not the case in places like the US.
Another aspect with the low testing is a matter of having enough beds to care for the truly critical. In Italy, if you have a mild case and get tested positive, you're quarantined and given a bed that could have gone to a more severe patient. Japan's reasoning is that even if someone has a mild case or is asymptomatic, the average Japanese person can successfully limit their own spread of the virus through masks and good hygiene, which allows the hospitals to dedicate full attention to the critical patients. Obviously this can all go wrong if the infected folks aren't being hygienic, but the fact that the majority of Japanese citizens are hygienic and wear masks may legitimately be why Japan hasn't had major death tolls yet.
