Does Apple use a base grid for iOS elements?

I am currently working on creating an iOS and Android app for my company and was looking at the Sketch library that Apple provides for iOS. While inspecting a few elements it looks like some of the dimensions are chosen at random. For example checking out the main state of the navigation bar has a height of 91px which is not a base of 8 or 4 and the dimensions inside are the following.

Does anyone have an idea how the team decided the dimensions of elements without a base grid size? Knowing Apple I'm sure there has to be a reason behind this.