While starring at the screenshot posted at Upgrade from 10.2.1 to 10.3.0 using Upgrader in Owncloud Web Interface i’ve noticed the following text:
The update was unsuccessful. Please report this issue to the ownCloud community.
This text looks plainly wrong to me in this situation and could cause the confusion for other users as seen above. 
Instead of reporting this issue to the ownCloud community the user itself needs to follow the advice given to continue with the update. Maybe this could already solve most of the confusion?