From the manpage for git pull:
git-pull - Fetch from and merge with another repository or a local branch
Git pull is identical to git fetch && git merge $remote_branch. He's saying that it prevents you from learning how branching works. So, if he were explicit, he should say 'Don't use git until you know how branching works at some level.', which is good advice. Not using git pull is a pretty sensational way to get at that nugget.
* If you `git pull`, you don't get the chance to diff between your local branch and what you just fetched and check if you really want to do that merge, using `git fetch` and `git merge` makes it more likely you'll do that check
* Getting used to `git fetch` means if you need to diverge from the straight `git fetch; git merge` workflow (because you want to rebase, or you have a high number of active topic branches floating around) you're already halfway there.
From the manpage for git pull: git-pull - Fetch from and merge with another repository or a local branch
Git pull is identical to git fetch && git merge $remote_branch. He's saying that it prevents you from learning how branching works. So, if he were explicit, he should say 'Don't use git until you know how branching works at some level.', which is good advice. Not using git pull is a pretty sensational way to get at that nugget.