China was extremely expansionist. It's just that over time they successfully assimilated (or suppressed) most of the regions they conquered, to the point where they and most other people think of them as naturally part of China (ignore what the Tibetans, Uighirs, and Mongols say, they're just disloyal).

That's a bit like saying, "The US never grew much beyond its current borders, so it wasn't expansionist."