It says nothing about only shading the small squares completely, so … how would you divide a square cake into two parts without a ruler?
And if you had four of these cakes?

@chris True. I guess I can’t think out of the BOX so here is My possible solution

That‘s the solution I considered.
(Interesting - I didn‘t get your answer until now.)

I think it‘s less „lack of outside the box thinking“ but more that our experiences make us presume usual constraints. This is often useful, except from when it‘s not.