$git pull origin your-branch is a shorcut which runs two commands one after another:

1. $git fetch origin your-branch
2. $git merge origin your-branch

So:

• fetch updates your-branch located on your local repository with the version of your-branch from the remote repository
• merge merges the current local branch in your workspace with your-branch from your local repository

So, if you're checked out on a different branch in your workspace (your-other-branch) and you run $git pull origin your-branch, it'll update your-branch on your local repository, then it'll merge your-branch from the local repository into your-other-branch in your workspace.

tdlr; run $git switch/checkout your-branch before running $git pull origin your-branch.