The OP says, under "Methodology notes":

> Non-binary and “other” genders are excluded from this study due to lack of sample size.

They haven't made this assumption, they've explicitly stated there was not sufficient data but acknowledged that other people not covered by the survey exist.

The app measures more than 2 genders but there's not enough sample to draw any conclusions.

Probably because intersexuality is so rare that there's not enough data.

intersexuality concerns sex, not gender, where non-binary, genderqueer, etc. individuals exist. The social construct of gender is what is being studied here

All data is data, if you want more go find or acquire.

Because performing math on Infinity is really hard.