> Java had a leg-up over C++ by several decades in having a concurrency story (at all) in the language.

While sort of technically true, concurrent code expressed in high level language was almost invented in C in the 1980's as the first Unix SMP devices took off (early multiprocessing work at the OS level was at the assembly level, Unix was almost alone in having a portable kernel and the need for SMP).

Java, coming along about a decade later from the same incubation environment, very much reflects that learning. But no, they did it right in Java because they had already done it in C.