It's not about using vim, it's about when you had to sudoedit a config on a server you visited the first time, and it had vim as default EDITOR, so you have to know how to exit it and open nano, or whatever you use. It's about exposure, exposure to many small things is a sign of experience, it is experience, to be precise. If they don't know small basic things, it's a sign, they don't have relevant experience. Can also check, if they have empty lines at the end of their files, know how to remove docker images from their machine, or get a TCP/UDP joke.