I take very little issue with the initial teaser (it wasn't a direct teaser for Halo 5 in the first place, and even if it was it came out long enough ago that it could easily have been something they scrapped, or even something they pulled together before the actual story was even finished), but i can understand why people would take issue with some of the more recent marketing. It's not outright lying, but it is a bit dishonest.
I'm not sure why Halo 5 would be the game that gets them to bring this kind of discussion to light though. Regardless to its present day quality (which i can't comment on), Destiny is a much better recent example of dishonest marketing.











