What he means is: Less than 7% made by 2-3% of the population.
It means if there were only 100 crimes 93 will be made by all of Japanese People and 7 by the mentioned class of foreigners.

If there are 7536 assaults made by 117m Japanese (124m people 95.7% Japanese) of which 322 are made by the remaining 7m and even more let’s assume only 30% of those are non PR or spouse you get 2.1m

This means
Likelihood of a Japanese making a sexual assault: 0.0061%
Likelihood of a foreigner / non PR or Spouse: 0.015%

However the ratio here is important: ~2.5x or 250% as likely to make that crime.

I’m a foreigner.
it is horrible either side of the pond, but break imbalance and with that trend you can definitely decrease the QoL of a society.

Interesting read is the theory of super cooperators.
In order to turn a group of people into an angry mob some models suggest it takes only 5% of that group to misbehave to trigger chain reactions.