Sharing via iMessage or Text using the Messages Action Menu item works by uploading your event to the WeekCal.com servers. WeekCal.com will store your event safely and generate a unique, personal web-link.
Only people you send the web-link to can view the event on WeekCal.com.
Receivers of the web-link get a small preview of the event and can tap on a button to quickly import the event into Week Calendar or any other calendar app.