The very first word in that article is “Android 12L”. 12L is not Android 12, it’s Android “12.1”.
See also:
“However, this cool feature has been exclusive to Google’s Pixel phones so far. But that’s set to change soon as Google has now fully open-sourced the Monet engine with Android 12L.”
So, that supports my believe: Android 12 did not include Material You yet, it was still Pixel-exclusive then.