I'm not sure if this author used an LLM, but I think you've misunderstood that paragraph. At worst, the line you're referencing is a tongue-in-check little introduction into a paragraph that describes the top-level differences in approach to serialization that the two libraries take.
deser might also just be deserialize shortened, and I was wondering if it was something focused on deserialization only. As such, I didn’t find a quick little note on the etymology to be a particularly egregious waste of words.
[0] https://facet.rs
[1] https://fasterthanli.me/articles/introducing-facet-reflectio...