According to US Census data [0], between 2000 and 2010, the City of Austin (meaning the city proper not the metro area)'s "African American (non-Hispanic)" population fell by 5.4% (a decline of almost 3,500 people). Over the same time period, its overall population grew by around 20% (from 657,000 to 790,000). That seems more consistent with what the article says than with the picture you are painting.
That's a good find, I'd like to see the 2020 census data but we're still waiting on that. At any rate, when you look closer at the data from 2000 to 2010, you see several trends:
- Black 18+ pop increased from 45.5K to 46.2K
- Black children pop decreased from 18.7K to 14.5K
- Hispanic pop increased from 200K to 277K (most significant demographic increase)
- White, non-Hispanic percentage decreased from 53% to 49%
- Asian percentage increased from 4.7% to 6.3%
Either black people in Austin had less kids from 1992-2010 than 1982-2000 (possible, given the stable adult pop numbers) or black families left for the suburbs or other cities entirely.
In 2010, Austin real estate was still quite affordable and the east side was not quite developed (article mentions a house could be bought for $100K there).
[0] https://www.austintexas.gov/sites/default/files/files/Planni...