By looking at the documentation one could think that the .version specified in Butane template files (.bu) should match z-stream from the RHOCP cluster.
This is actually a specification for Butane itself and doesn't relate in any way to RHOCP, see [0]

[0] https://coreos.github.io/butane/specs/

Documentation bug is from RHOCP 4.8 onwards (since Butane was introduced)

Look at documentation specific to y-stream RHOCP version at chrony configuration section. See [1] (4.8 doc):

[1] https://docs.openshift.com/container-platform/4.8/installing/install_config/installing-customizing.html#installation-special-config-chrony_installing-customizing

1. Look at the docs
2. No mention that RHOCP z-stream is not in any way related to .version in .bu files examples

See above

Should be highlighted somewhere that z-stream is not related.
I.e. RHOCP 4.10 docs should say something like "please note that .bu files .version needs to stick with x.y.0"