How is this relevant to anything
2) "More likely to behave similarly" is a considerably wider net than just crime rates
3) I think the mainstream view is that East Asians of all stripes commit considerably less crime than average. It's certainly true of violent crime, which is something I've looked in to.
This point was used to defend Japan's justice system as being far more benign than the US.
However, Japan's justice system may in fact be far more unforgiving that the US' if Americans are, in general, more likely to commit crime. Which is perfectly fair point to make (although inconclusive for various reasons).
If (for whatever reason) Americans are more likely to commit more crimes, they are, all else being equal, more likely to be in jail.
Of course many things can be true at the same time. Japan can have a brutal justice system and have a very docile, law abiding population. Maybe the brutality caused them to be docile. Or, America can have an abusive justice system, and a population that needs to be more incarcerated than others.
Either way, the criminality of the Japanese is a relevant factor if America's incarceration rate is made relevant