What does UserA committed with UserB 13 days ago on github mean?

Question

I am interested in knowing which one of the two users made the file changes when github lists both. The git record contains only UserA however.

Answer 1

Another one of possible reasons behind this happening is by using $GIT_AUTHOR_NAME and $GIT_AUTHOR_EMAIL env variables.

When these variables are set, they override the author part of every onward commit no matter what user.name and user.email config values are set locally. In this case, when you hit git cat-file -p HEAD, author shows value of $GIT_AUTHOR_NAME and committer shows value of local user.name configuration.

So you'll need to remove lines that export these variables in .bashrc or .zshrc, or if you want to preserve those lines but just don't want this thing happen, insert unset GIT_AUTHOR_NAME && unset GIT_AUTHOR_EMAIL before running git commit.