Broadly, I must say I believe that Dan Meyer would have done much better if he'd explained just how that illustration connected with the math of filling glasses of various shapes and dimensions (perhaps including some discussion about 'rate of flow of the water' as well). There is also the possibility of doing some 'practicals' at the same time.
For one thing, he'd have at least in part refuted Robert Hansen's charge of "math avoidance". (I believe he [Dan Meyer] must be aware of this criticism).
There is definitely plenty of useful math for students to learn from the example - most of which is not immediately evident from the pictures shown. Showing some of that would I believe have been most useful for math teachers who read the Dan Meyer pages.