Because they have gone on public record with those numbers and as of yet, no one has refuted them.

Do you have an alternate source of user level data that breaks down average vs. outliers and that ratio that you feel is more accurate?

The free tier is 100 queries per minute for an OAuth logged in client per the public statement, and that number has also been stated by a few 3rd party app developers.

That is a lot for the average user, especially for a well optimized app.