The decision pickup notice clearly states that USCIS will not notify you of the decision before that date. Also, there are many users on this forum who received a letter between their interview and pickup date notifying them of decision delay and to expect it in the mail instead so its possiblePerhaps they sent a decision in mail and you'll get one in person as well?
I think they typically notify people about delay in decision via the phone call and not through the letter.
Good luck today on the pickup. I wish you an approval.