The symmetry, the beautiful simplicity of the solution, and the fact that 80 percent of the participants were effectively blinded by the boundaries of the square led Guilford and the readers of his books to leap to the sweeping conclusion that creativity requires you to go outside the box.
The idea went viral (via 1970s-era media and word of mouth, of course).
It's an interesting experiment, but the author's conclusion cannot possibly follow from the results of it.
your conclusion: that the second experiment disproves the theory that thinking outside the box is useful in solving problems, is itself a fallacy.
They are much more common than you probably think.*From Inside the Box: A Proven System of Creativity for Breakthrough Results Copyright 2014 Drew Boyd There are many theories of creativity.