Hello,
I've never seen anything like this before. I think I know what happened. You can see some rebar bent back, for whatever reason that was done. I believe the bending back of the rebar was done when the concrete was barely hardened, and that's how these cracks were formed. If you look at the spot where the rebar penetrates the concrete, the hole is open to the outside, which is exactly the reason for my theory.
The neighbor's formwork has nothing to do with the crack.
As the client, I would freak out. But what good would that do?
The reinforcement steel creates a fixed connection in the slab. It should be checked whether this connection is necessary for the wall's structural stability. For normal heights and loads, this is constructive reinforcement. The bond in the concrete was disturbed, and the rebar has hardly any effect anymore. After all, walls are also built by laying blocks, and the slab is simply placed on top.
The only thing I can recommend is to have the structural analysis shown and explained to you.
Regards