Had this occur yesterday.
They found this under the slab in the 3/4 " cold water line.
That sucks. I assume that is a Nail Hole?
I had a similar issue years ago when I redid a powder room. I put up all new sheet rock and had it nailed, taped, and spackled when I decided to put one last nail in a spot I thought was bulging a bit. Of course there was the water pipe traveling thru the middle of the 2x4 I was nailing into and the tip of the nail pierced the water pipe causing me to have to rip out half the wall, repair the pipe, and redo the wall again.
Its 6 " away from the wall and down about 10" under the 6" concrete slab. The plumber didn't have a clue, but he called me over and told me to put my hand under the slab and feel. IT was a wow how in the hell moment, then they cut the slab and there is was.
That is odd. It looks like a fresh hole
...They just don't know as it was under 6' of solid concrete.
I am sure you meant 6 inches not 6 feet. Something to consider: If you have a device that is vibrating nearby (like a washing machine), the vibration of the machine may cause vibration on the pipe which in turn can cause micro cracking of the copper. The leaking hole can be very tiny in the beginning and you may not even notice anything. But as the vibration continues, the hole will grow. It is also possible that a hard gravel piece from the concrete could have been trapped between the top of the pipe and the concrete slab and due to the vibration the gravel ate into the copper pipe. Just a thought.