What determines precedence for release dates?

Heavy Rescue: 401 is a Canadian series. The latest episode premiered tonight in the US but premiered back on February 9 in its native country. I added the US release date just as a data point (which is the entire point of accepting release dates for each country), and was surprised to see that the US date has taken precedence.

Why does this happen? Shouldn't the country of origin take precedence? Or does IMDB just do this behind the scenes because it detects I am in the US, while people in other countries see different dates based on their location and the availability of data for their location?

This page should show what I mean:

Heavy Rescue: 401 Season 5