Halo: The TV Series is not meaningfully the same story as Halo: The Video Game Series.
It has some similar characters and concepts, in the same way that most fanfiction has characters and concepts that more or less resemble the original work.
But that's very much what it is: fanfiction. And *bad* fanfiction, at that.
Why couldn't they just tell the interesting story that was already there? I really don't understand.