This is "old Internet" style fun territory (along the same lines as the Tom7 fun, if not quite as deep). I felt that the olive oil + fingerprint + phone screen was a really nice way to illustrate the core concept. Especially clever because it used something common and annoying to help describe how the plotter does its thing.

Before getting further into the article I thought maybe he was going to show how to use the plotter to control the oil smearing technique, which honestly would have been kind of cool.

There are very few TFAs I upvotes before opening TFA. But with such a title, this is one of them...