[cge]

I TA'd BE/CS/CNS/Bi/etc 191 years ago, we had some freshman in the class, and there was definitely the expectation they'd have some familiarity with differential equations; for example, the mass-action model of chemical reaction networks relies on them.

These sorts of classes tend to get students in a broad range of levels, and I think there's the expectation that they'll figure out whatever they're unfamiliar with. I doubt this class is targeted to graduate students, but Caltech classes tend not to have a graduate/undergraduate distinction.

[Demonoculus]

I'm hoping this is a typo '191 years ago'. Don't mean to sound pedantic just interested when this was. My friend was in Caltech for his MS + PhD in Electrical engineering from 2008 onwards. I think he graduated in 2014-ish.

[cge]

Not a typo, just an amusing ambiguity: the course was 191. It would have been around the same time as your friend.