It to me implies a wood screw or rivet head. as an object that would have the shape and mass to cause a similar fracture pattern, The circles of shattering would be the peaks of the impact displacement ripple, making an initial displacement, then the distance between shears in the glass decreasing due to loss of energy thanks to loss of intensity as it spreads away,
There is some math screaming out in the back of my head about how to calculate the delivered energy, but i'll retire that for the night, but it would be along the lines of energy to shatter the glass from a 0.5mm surface, plus the energy to displace the plastic lining past its elastic phase, assume for non radioactive elements, and leaves a good idea of the mass,