I think it depends on how public and how many contributors you have to a feature branch. I think author has the assumption that there is typically one dev per feature branch.
Once a feature branch is being worked on by multiple devs (and hence multiple feature branches forked off), it is a public branch and should use a merge based workflow.[0]
I personally use a rebase workflow on private branches before merging since it makes for a cleaner history. I've seen devs merge a branch with 100+ merge commits and it absolutely destroys git history.