No – that shouldn’t be the case. Unfortunately it’s not clear which mirror you were looking at.
No – we don’t deliver any binary add-ons via a Kodi repository; we include them with the package and build time and deliver them via APT.
We host our own Kodi repository for better uptime and reliability and also out of respect. We are a separate project, so want to provide our own resources and bandwidth for our userbase.
We synchronise every hour with the Kodi add-on repository, so OSMC users will never really be behind with add-on updates.