It seems that by using auto-fit, grid is essentially becoming one-dimensional. To my amateur eyes, most of the examples given in the article “Look Ma…” can be accomplished with flexbox (except for the one that uses grid-auto-flow: dense;). So, why is grid preferable in these examples?
For many layouts flexbox requires additional wrapping elements where css-grid does not which leads, often, to cleaner lower maintenance HTML.
Frankly, as long as you understand the feature, possibilities and limitations of both layout methods it’s not a question. You use whichever fits your requirements the best.
There’s no reason to prefer on over the other unless one of them can’t do what you want.