Stackoverflow thank you for the dislikes - I don't get why but still.

Here is the answer:

The machine (in my case linux) has to use the DNS server of the MS AD. However since I only changed it in the /etc/resolf.conf on my linux machine this change was only termporary. When I restarted my linux machine, it changed it back to my router. This lead to the error message which in my mind is completely garbage since it doesn't really have anything to do with the actual problem...

A quick way to confirm if the machine uses the MS AD DNS: ping your domain - in my case ping schooliead.local