Looking up something else in the manual and stumbled on chapter 6, section 2 clearly stating you can self service your Mazda without voiding warranty. Save receipts.
Looking through the 2016 Warranty Information Booklet. Page 32: "but Mazda cannot deny warranty solely for the lack of receipts or failure to ensure" that you do all scheduled maintenance.
You should send Mazda Corporate an email about this d-bag.