You can {% if not 'raspi' in system %}, or get help on installing{% endif %}.
Run this command in your terminal in the directory the iso was downloaded to verify the SHA256 checksum:
echo "{{ releases.checksums[system][version] }}" | shasum -a 256 --check
You should get the following output:
ubuntu-{{ version }}-{% if system != architecture %}{{ system }}-{% else %}preinstalled-server-{% endif %}{{ architecture }}.iso: OK
Or follow this tutorial to learn how to verify downloads.
{% else %}Please check the SHA256SUMS page for the checksum numbers.
{% endif %}