The Man in Black is looking for the final piece of "the puzzle" (some quest that originated with Arnold) and after talking to the little girl in Las Mudas he winds up at the blood arroya with Armistice (snake lady). He then thinks the reasoning behind her tattoo is the next clue he needs. Armistice later tells him the story behind her tattoo has to do with Wyatt.
My question is this: Didn't Ford just recently create the Wyatt narrative in response to giving Teddy a good backstory and ultimately assisting him in keeping Dolores in her loop? How does the MiB’s quest revolving around Arnold (whose been dead for decades now) get connected to a recent addition to the park by Ford??