Brake pads worn out on the rear

Z Spec

I just took my car to the dealership for an oil change and they told me that my rear brake is at 2mm, while my front is at 8mm. I thought this was odd since the brakes usually wear out on the front before the rear. I asked why is that the rear wore out first before the front and they said that the oem brake pads in the rear are less thick than the ones up front causing it to be worn out on the rear first.

Is this true? Or is there something wrong with my rear brakes?

My Z has only 21k miles and does not see the track.