I would say, based on an estimation from my observation, that they held at least 5 mm proud of the tread base. They seem relatively new, with plenty of wear left on them.
I suspect that many of the tires sold in this way come from vehicles that will no longer be driven, for various reasons. If I were not able to employ them, they would be wasted along with the car from which they were separated.
And rest assured, they are in very much better shape than the tires they replaced. I cautioned the mechanic to be careful about the loose strands of steel that were sticking out of the carcass.
There's a use of 'proud' I haven't seen in a while.
Well played!