Both you and the OP are incorrect. The file is not included in the app (only referred to), but is only downloaded by iOS itself - or anyone who points a web client directly at it, of course.
Looks like a signed json file found at `/apple-app-site-association` on sites that support it (eg. booking.com/apple-app-site-association, nytimes.com/apple-app-site-association, &c.)