The author is doing what a non-sophisticated user would be doing, or would want to be able to do, and estimating calories based on a photo has been an often-cited potential or promised AI use case in recent years years. It makes a lot of sense to test current general-purpose AI’s performance on it as a reality check.

It also exemplifies how current AI offerings are still quite limited in their capabilities, because one would expect that they’d do the intelligent thing on their own that you had expected, instead of the user having to come up with a working methodology.