That's not exactly true... There's way of tracing coins other than through following their addresses. Sometimes outputs have similar characteristics such as size, timestamp when moved, and their eventual destination. If 5,000 coins are all put into ChipMixer at the same time and 5,000 coins end up moving all to the same final address however many weeks later, its safe to say those belong to the same owner.
Regardless, Chainalysis didn't actually use the word "Chipmixer," they focused more on Wasabi wallet, and this image demonstrates just how futile their efforts were: