I'll hold my hands up and say I haven't tried the default Magento 2 backup/restore method as I don't trust it. But only because I want to see exactly what is happening. Which is why I recommend using a shell script you've put together yourself. But that's for another discussion.
In answer to your question
https://devdocs.magento.com/guides/v2.3/install-gde/install/cli/install-cli-backup.html
This command enables you to back up:
- The Magento file system (excluding var and pub/static directories)
- The pub/media directoryThis command enables you to back up:
- The Magento file system (excluding var and pub/static directories)
So depends on what they mean by Magento file system. Based on the above info I would say yes - the /blog
would be covered. However I wouldn't rely on this until it's too late. Have you got a test server you can experiment on?
But also did you spot the following note:
Deprecation Notice Magento backup functionality is deprecated as of 2.1.16, 2.2.7, and 2.3.0. We recommend investigating additional backup technologies and binary backup tools (such as Percona XtraBackup).
So depending on what version you are running you might not be covered.
Update
Shell script loosely based on this
https://github.com/MagePsycho/magento2-db-code-backup-bash-script