No worries, that is still effectively a read-only access.
As you can see, even the "create" subcommand is marked with "readonly", which basically means it cannot create anything :). You can verify that, if you want, by logging in into that account and trying to create or modify things.
As a side note, I personally use the built-in "readonly" role for Harvest. It allows to read anything, but not to modify or create.
Recent versions of Harvest add additional capabilities, which won't work if you follow the old guide and only add those listed commands to the custom role. Using the "readonly" role should always work, even when Harvest gets new features. Obviously, if you want to limit even the read access to only specific sections, you need to use the purpose-built role.