How does one write an article which summarizes the process of building a machine learning model, and not discuss cross validation? Not a very good article, to be honest.
They hint at withholding data ("The same logic applies when it comes time to splitting our data into training and validation sets"), though they don't outright mention cross-validation. Seems like a bit of an oversight for an article about building ML models, I agree, but the article seems like it's mostly surface-level.