Let's Encrypt certbot validation over HTTPS
As reported in https://community.letsencrypt.org/t/shouldnt-verification-via-dns-record-be-a-priority/604/47 the letsencrypt.sh updater supports validation via DNS. Few updater scripts seem to have implemented this. However, the HTTP method is the simplest to implement for initial configuration.
The script you have may use TNS SNI or Proof of Possession of a Prior Key for renewals. Specification can be found at https://datatracker.ietf.org/doc/html/draft-ietf-acme-acme-01#section-7.5. If this is the case you won't need to have HTTP enabled.