I'm not sure what the 'critical' stuff is either or what the details of Airbus' network hosting and knowledge compartmentalization strategy is, but you're not going to run a globally distributed manufacturing business with complex supply and maintenance requirements without having technical specs, CAD files, diagnostic criteria customer records etc sitting on computers connected to the internet.
It seems there is a misunderstanding over the classification of 'critical' stuff.
We may all have a very different definition.
All I know: the second your are connected to internet, you are cooked.