Is this what is expected of how to cite sources? Because if this is the expectation nobody does it.

There are two cases and only one is an issue for citations: - Mononoke was directly consulted and not attributed - Concepts were reinvented or used as a derivative (Sapling cited Mononoke and implements something similar)

For one I know Sapling, Git, and Jujutsu, but up to today I have never heard of Oxide or Mononoke and I am not exactly compelled to look up the research papers of any of them, at most I read through their high level documentation.

To be clear, Mononoke is the server-side part of the Sapling system as deployed at Meta. Scion appears to be very closely inspired by Mononoke.

Sapling does a bit more than cite Mononoke. And Oxide was not involved in Mononoke's development. These are kind of details that would not be expected of a casual user. However, when valuations soar into the trillions, we can expect companies with dedicated writing staff to communicate attribution properly.