Where to create a message?

Hi

I'm trying to write my own application code on CC2538. when I tried to create a Message for keyboard interrupt found below routine in sample applications (samplelight for example)

interrupt_keybd() -> hal_key_int_keys()  -> hal_keyCback_t ->  OnboardkeyCallback() -> Onboard_sendkey ()

I need to know if I understood the way right or not? why the way is complex like this? Can I create the message directly in my interrupt callback function?

Thanks

Behnam