Conclusion: Fear not, because this (and several other) achievements are glitched in a good way, making them almost impossible *not* to get. You should be able to get all 19 achievements in about 10-12 hours of playtime.
Assassin's Creed III : The Tyranny of King Washington Episode 1 Review
2 April 2013
Excerpt: Downloadable content is always most successful when it takes a game and characters that you know well and puts them in a new, ideally implausible setting – like Red Dead Redemption’s Undead Nightmare, or Borderlands’ Zombie Island of Dr Ned.
Excerpt: I am pursuing a man in a tricorner hat through the streets of colonial New York. In the top-left of the screen, Assassin’s Creed III instructs me to chase him. In smaller text just below it, there is a secondary objective: ‘do not shove or tackle anyone’.
Excerpt: Late last year Assassin's Creed divided opinion more than any other game in recent memory. While some hailed it as a true next-gen gaming experience, others felt it was little more than a simple gameplay concept wrapped in stunning visuals.