Depending on which article you look at, you can see things such as the stunning, vivid rotating 3D model showing the optic lobes, or elaborations on what the model captures: it has mapped 139,000 neurons and 130 million synapses. I don't think that quietly picturing a fruit fly in your head executes a true simulation of those details.

I do think, in some cases, there is such a thing as thinking being equivalent to simulating (e.g. a calculator) but this isn't one of those.