Author here. It's just a matter of personal preference. If you're proficient with Ansible then I'm sure you can achieve the same task even quicker. But to me, shell scripts are a more natural & faster way to get going for single-server setups and I always have a hard time with Ansible yaml syntax.

Ansible has some undisputed advantages (e.g. idempotence) and if I had to recommend Ansible vs my approach, I'd always recommend Ansible. But for my personal needs (single-server rails apps), I prefer shell scripts.