It’s by country of birth. So that applicant with the long wait could be from Canada if they were born in India.
see https://travel.state.gov/content/travel/en/legal/visa-law0/v... and click on the latest bulletin. You'll probably want to look at the employment-based green card waiting list.
For example, a EB2 applicant born in Canada filing today would be backlogged because the date of filing is listed as 01JAN23.