I think so too.
I attribute it to a faster power up sequence. The sensor detects, but then it has to power up the Z-something radio... Zigbee is faster to power up in my house.
I have a lot of motion sensors, 2 brands of ZWave, 2 'brands' of Zigbee. (Iris v2 and v3 but they are from different manufacturers.) The LED within each flashes on motion. The LED comes on, the resulting reaction of RM + Z-device to turn on a light always seems the same, ZWave or Zigbee. Before the LED is off on the sensor, the room light is on. About 250ms (1/4 second). However... where I see the difference is in the gap between movement in the sensor's known window and the LED flashing on.
I have various places where I can 'sneak up' on a sensor. One giant step and I'm in it's detection window. For Zigbee, I can see the LED almost instantly, and thus the room light comes on, 1/4 second later. For ZWave, I can see the delay before the LED comes on, and indeed the room light comes on 1/4 second after, but that up front delay is very obvious to me. Again, I attribute it to the Radio's power up readiness.