Ruby Challenges - The Wiley Word Square

This topic is for the [The Wiley Word Square][] exercise in the [Ruby Challenges][] trail. Post any questions, corrections, or pointers you have to share with other Upcase subscribers.
[The Wiley Word Square]: https://exercises.upcase.com/exercises/the-wiley-word-square
[Ruby Challenges]: https://thoughtbot.com/upcase/ruby-challenges

In the exercise’s example, “cat” is the first row word, and “cab” is the first column word. The examples in the linked Wikipedia article has the row and the corresponding column being the same word. Please clarify if we only need to find valid words, OR if row[x] should equal col[x].