The cases outside of China would be people healthy enough to travel at least so there is that bit of preselection of the sample. I suppose once transmission starts to take place outside of China things might change from that sample.
That is a factor in the mortality rate, to be sure.
Our health care system is likely more advanced. Therapies are more prolific. Medications are likely more diverse.
People who travel are more likely to have pretty good access to top level treatment.