What decides when the git reference-transaction hook runs?

Question

I have git 2.28.0

I have a remote branch and a local branch that both point to the same commit. If I checkout the commit or the remote branch I see the reference-transaction hook run, but if I checkout the local branch I don't.

I can't find any reference to this behaviour in the docs. Is this expected? and if so why? and where is it documented?