Obviously parent is not claiming that Nim invented the concept of reference counting. They're saying that it's a recent addition to Nim, and Nim's other memory management strategies have been part of the compiler for longer.
Swift and Obj-C's ARC system relies on atomics and their associated issues (explained well here: https://news.ycombinator.com/item?id=15046481).
Nim's ARC system relies on ownership rules that require a single thread to "own" any ARC-managed memory which removes the need for locks or atomics in the reference counts. That eliminates the non-determinism of locks & atomics when doing the RC accounting, overall improving latency and performance. Move semantics increase performance and enables "giving" ownership of ARC-managed memory to another thread.