Why is "wpt_create_widget()" called with standard function call and not by using "add_action()" or "add_filter()" ?

It seems that all the functions and function calls we are putting into "functions.php" follow a standard format, where they are called using "add_action()" or "add_filter()", so that they have a certain "hook" and can be called at the proper time.... yet in this video, we just do a standard function call for "wpt_create_widget()".

Why can this be called with a standard function call, and yet other things need to be called using "add_action()" or "add_filter()" ?