Is Criptext really opensource?

I was trying to review the self-hosted version and only can find the mobile clients, not the backend.

on your website, https://criptext.com/en/about, (throughout many pages on the site) it states

_With Criptext we’re giving control back to the user. We don’t ask for trust, but rather promote people to verify, which is why **we’ve made Criptext entirely open source.**

Is this another Protonmail/mailspring, where the front-end is opensource but not the backend? If so, that is a shame