Why do the assumptions of this question not line up with the test cases?
Assumption: "Given a 2D board..."
Violation: Last executed input: ["aa"], "a"
What the hell? The board isn't 2d..
Also, is the example intended to throw you for a loop? The example would suggest that each cell only has a single character, but for some reason this test case has a 1d board with two characters? Are we supposed to assume some 'unreliable author' BS about the person asking the question?