As if inference exists in a bubble. Driving a car from point A to point B costs $0, as long as you exclude the cost of the car or the fuel you purchased before you were at point A.

I believe that, equally it's so unverifiable that it's a point of faith.

I'm not suggesting it's an outright lie, but rather it's easy to massage the costs to make it look true even if it isnt. Eg does GPU cost go into inference cost or not?

I would be surprised if they are being honest.