This can't be true. It would depend on so many factors such as the specific metal, the shape of the metal where it comes into contact (a point, an edge, a curve..), the force of contact, etc. Gorilla glass isn't some mystical impervious material.
---------- Post added at 10:47 AM ---------- Previous post was at 10:40 AM ----------
Just received my ultra-slim Moko. For $6 it's nice but I really wouldn't recommend it for a few reasons.
1) As mentioned before, the metal piece on the cover could potentially come in contact with your screen and scratch it.
2) When closed, the cover slides around. This is very obnoxious when you are walking around with your tablet in one hand. Basically, if you hold it vertical, the cover slides up while the tablet slides down from its weight. Over time this is just going to get worse as the cover loosens.
3) I'm having lots of trouble making it stand up in both positions and stay put. The triangle fold does not hold, I think due to poor choice of the size of each edge of the triangle. Maybe with time it will get better but it hasn't so far.
Overall this thing is just flimsy, although it does look and feel nice to the touch.