Recreate a painting with Bootstrap grid / adding <div class="row">

https://www.codecademy.com/courses/learn-bootstrap/projects/bootstrap-grid-painting

Im in the middle of making a basic project


Comparing with both above pictures, one big difference between both of them is whether putting another * div class=“row” * or not.
I can’t understand why I have to add * div class=“row” * on 16 and 22 lines.