> They can both be private methods in a single module, the example still applies fine?

It does, but you're now looking at an edge case that rarely arises in practice in a well-maintained codebase, and certainly not one to design your entire branching/merging/CI strategy around.

If your codebase is a spaghettified nonsense then the problem arises much more often, and so I can understand the use of merge trains/whatnot.