Creative masons?

This section of wall in our village church intrigues me. It is the wall of the south aisle which was added to the original church in 1440. Were these medieval masons deliberately making a pattern, a decorative area of the wall, or were they just using whatever material came to hand? There is another similar random area the other side of the window, otherwise the walls are just plain flint.
I like to think that the masons were being creative, working on their own initiative. I love to imagine them building this wall. What were they wearing? How did they speak? Were they brought in as travelling artisans especially to do the job or were they local men? We'll never know, but what we do know is that they left a beautiful and durable legacy.