the command to checkout the master that I showed you is a shortcut for further steps that Git automatically does for you.
git checkout <branch>
- It checks whether or not the branch already exists in the local area of your repository
- If the branch is already there, git just does a checkout for this branch and nothing more.
- If the branch is not there git looks in the remote area and checks whether or not the branch exists.
- If the branch exists in the remote area, git does a "git checkout -b <branch> <remote>/<branch>" and creates a reference between the new branch and the remote.
- If there are two or more remotes with the wanted branch, then git can't decide which one it should use and it prints an error. In this case you have to do the full checkout command (see nr. 4) by your self.
In your case the master branch was already there. So the simple command "git checkout master" did only checkout the local master and not the master from the remote. If this old master branch is part of the history of the remote master you can easily do a git pull to get the last version. That's what you did.