Semi-correct observation. You could think of it as a ZeroMQ broker that supports the pub/sub patternz, yes. Difference is it's centralized (with support for HA), adds security, gives you monitoring, supports multi-tenancy and horizontal scaling allowing to connect multiple clusters. Benefit of using broker is that service discovery is a no-op.

Also, NATS has client libraries for many languages that adds request/response semantics on top of the pub/sub semantics.