Hey Laura,
Thanks for reaching out about this – you are indeed correct about using the “default-template.php” file that is included in The Events Calendar. This is the one and only default-template.php file in our plugin suite, and it is the “Default Events Template” that is referred to in the Events settings page, in our documentation, and so on…
I hope that information helps. To clarify, The Events Calendar is the “core” piece of software here. Events Calendar Pro and literally every other add-on we sell is, well, an add-on to this core. So Events Calendar Pro just “inherits” a lot of its code from The Events Calendar, and uses many of the template files that exist in it.
default-template.php is itself a sort-of “core” template file, and so yes, it only resides within The Events Calendar. You should NOT be concerned about a different route here – what you are doing is correct 🙂
Cheers!
George