I’m guessing the author is getting some kind of referral to send them to that other site that hosts grafana. Because home assistant has a 3rd party app for grafana built in. Granted it would be a few more steps than they outlined, but it’s also not sending your data to some random company.

No particular reason. Just chose one and went with it.

FYI, for step 3 you should be able to do a “docker compose pull” with the same effect.

Edit: and on step 8.2, to minimize down time, you can also do the pull before stopping the containers.