Hi there, Johan! Thanks for getting in touch and welcome to the forums. 🙂
Good question. The iCal export option below the calendar will export the events that are displayed on the calendar in the current view it is on. So, for example, if you have the Filter Bar plugin installed (which you do), and select multiple categories in the Filter Bar, the export button belie the calendar will download only the filtered categories that are displayed on the calendar.
Does that make sense? Let me know if that helps clarify things a bit.
Cheers!
Geoff