This article is not based on serious data. Companies do this kind of thing so they get lots of press and unearned publicity. Somebody just took the change from the last census and multiplied it to the end of the century. This isn’t science, it’s a bad Excel spreadsheet. Growth rates are not constant or predictable that way. In fact, Austin’s growth rate currently is receding.

Source: https://www.macrotrends.net/cities/22926/austin/population