iCal feeds don't bring you into the site. The whole point of Facebook is to be a walled garden that discourages you from going elsewhere. You're lucky they are not like X and deprioritize external links. Or maybe they do, I have not tested it myself.

https://theoatmeal.com/comics/reaching_people

I would click the link in the event to go say happy birthday to the person! I guess I wasn't the norm though aye, it's big numbers that matter