That proves that exclusionary zoning was around in 1971, but not that it wasn't used earlier. Massachusetts amended its constitution in 1918, literally one year after Buchanan, to enable cities to impose zoning. And the idea of using it to create racial segregation was specifically discussed at the time [0]:

Of particular concern was the fear that zoning would bring about racial and socioeconomic segregation in Massachusetts, which need not take the form of racial tests, as zoning could just as easily bring about segregation by regulating who could afford certain neighborhoods by income. Pro-zoning advocates... [went ahead anyways]

[0]: https://www.cambridgema.gov/~/media/Files/officeofthemayor/2...