I read the numerology thing on a website about the final chapter and it's just something to think about, but it wouldnt surprise me if Isayama did it on purpose considering the nature of the episode and the symbology behind everything that happens. "OUR BATTLE IS ONLY GETTING STARTED" at the end also has some fans speculating there may be a chapter 140 or possibly even a sequel. Anyways, 139 wasn't a bad chapter it was very good, amazing even.... but to have that as the actual ending just doesn't seem right.
The anime adaptation won't be caught up to the manga until 2022, but you can watch all the way up to the final season part 1 if you do decide to binge watch :)