I don’t understand any of them. Normally even when I’m not really familiar with a tool, I have enough background knowledge to understand why it’s funny e.g. Scheme and Haskell jokes or something. I do use basic git regularly and all of this is over my head. I don’t know if that speaks to how complicated and unintuitive some of the advanced stuff is?
The context here is the statement that "its UX is famously... interesting". You don't have to understand anything other than how wildly inconsistent the git CLI is.
The second one is about how Git uses the word “checkout” for three unrelated operations, violating the Unix philosophy.