Not an Android expert, but this is how it seems to me.
It's Google's responsibility to implement the hooks in a secure way, so that an app that is registered e.g. for the "call" hook cannot prevent the call from taking place.
Seems that somewhere in there, someone messed up.
Re:Pixel prevented me from calling 911
by kuschku on Thursday December 09, 2021 @12:04PM
(#29499944)
The issue is that you might have a device where emergency calls have to be routed through a VoIP app, per legal requirements, e.g. if no cellular emergency calling is available (e.g. on voip-enabled wifi-only devices, or on voip-enabled devices in locations without cellular signal))
In software I write, the logic for 'emergency' priority events doesn't go through the same call chain for this reason.