I can't speak to what libraries you used, but both techniques have been broadly used in common practice since the 1950s. According to the "History" subsection in Knuth TAOCP v3 at the very end of 6.4 (whose very first edition written in 1972 covered OA with various probe/collision strategy ideas), both open addressing & separate chaining were co-invented at IBM in 1953/54 by Luhn & Amdahl. You may be confusing the Celis 1985 Robin Hood hashing work with just the open addressing part? Anyway, as you say, it may be a strained example/analogy. "OO" & "concurrency" both have a lot going on, too.

Anyway, like the "major" modes of hash collision resolution, reference counted GC has also been around concurrently (haha) with ref tracing GC since the dawn of modern computing. Unix hard-links (& other things) codify ref counting into filesystems.. Python has always had ref-counted GC, older Lisp more focused on tracing GC, etc., etc. Popularity measures are notoriously difficult.

Mostly people like to abbreviate { like having a search $PATH instead of using /bin/foo everywhere }. The whole point of abstraction is to neglect details. Neglect naturally leads to forgetting (or never learning/knowing). Ignorance leads people to cross-talk (or worse willfully misinterpret/project). Cross-talk leads to suffering. Yoda out. ;-)

EDIT: Also, speaking of abbreviation & clarity, in Nim "arc" has, at least until this writing, always stood for Automatic Reference Counting, not Atomic Ref Counting as seems the more rusty terminology and is vaguely suggested by @miguel_martin, to whom I originally replied with an "arc/atomicArc", though it seems like, in Nim 3, it may become both Automatic & Atomic, but probably not changing its abbreviation to "AARC".