It actually doesn't matter. If you chose the link and it goes to your calendar, it should also show up in Fantastical as long as you're viewing the same calenders in both the built in Calendar app and Fantastical. In Fantastical, go to Settings>Calendars and make sure you have the same calendar selected as in the built in app.
I use several different calendar apps but, as they all pull from the same informaton, it doesn't matter which one I enter the information on. I can see it on which ever app I look at.
Best of luck.