ASF4 reference manual provides description and example of External IO Interrupts implementation done without Event Driver. I also found similar example API code after configuring and downloading configuration for the SAME70-XPLD board. After proper re-configuration of the pin to match pin used for the on-board button and placing this code in the right file the project did not trigger Interrupt.
After trying different variation of the same approach I came to think that this path might be not working in ASF4 because it might require the Event System Driver to be called to process any external Interrupt.
The following made me think this way - I found example of using External IO Interrupt in ASF4 - the SAM D21 Event System example. It does trigger interrupt driven input from the button but here this is done using Event Driver.
So the larger question is as follows, in ASF4 :
can the external interrupts be processed and implemented using the direct registration of User Callback function (as per Chapter 19 of ASF4 manual) WITHOUT registration with Event Driver (meaning that both approaches can work - with or without Event Driver) ?
the External Interrupt will only work in ASF4 if the Callback is registered with the Event System Driver and not otherwise (which means the Ch. 19 example is wrong)?
This is important topic to de-mystify ASF4 so please clarify...