Assuming there weren't extenuating circumstances that prevented the flight attendants from doing pre-landing checks (like turbulence), then it was a mistake that shouldn't have happened, but it's not a huge deal. The FAA and airline policies and procedures are designed under the assumption that they will be executed by humans, and that humans will make mistakes from time-to-time. It doesn't hurt to report any such issues so that if there is a pattern of mistakes then the pattern can be identified and addressed, but a single mistake on a single flight isn't the end of the world.