Board Thread:Manga/@comment-29098965-20160719220900/@comment-27441457-20160719225919

I've heard from some fan translators that the word Zeke uses for "brainwash" when speaking with Eren bears the same connotation as our use of the word when referring to how commercials or propoganda "brainwashes" us rather than literal mental manipulation.

My guess would be that Grisha's ideology of humanity in the walls being the "good guys" was picked up by Eren, something the Warriors would strongly object to for their own reasons. Thus, Grisha indirectly "brainwashed" Eren into being against the Warriors and their cause.