This descriptions does not sound like it's about something that is "virtually unbreakable" : "The sample looked like an ordinary piece of glass, 4 inches square and transparent on both sides. It’d been packed like the precious specimen its inventor, Adam Khan, believed it to be—placed on wax paper, nestled in a tray lined with silicon gel, enclosed in a plastic case, surrounded by air bags, sealed in a cardboard box—…
It may very well be "virtually unbreakable" for the use case of something that's supposed to survive the rigors of life as a display for consumer electronics device. Breaking it, of course, would be something that any device designer would do in the course of characterizing or evaluating it as a component for a new product. Whether that would have been done on the first sample is something that's strictly between the…
It's all fine and good if your device can survive a drop from 1m onto a hard floor without cracking or chipping, but if a fall from 2m then results in a cloud of razor-sharp glass flechettes, that shred all flesh in a 5m radius, you're probably not going to want that particular screen treatment in a consumer product.
But this test material was not supposed to be used for that, I guess. I'm not sure how they were supposed to evaluate it.
Personally, I'd want to do all of the following:
Put it in a rock tumbler with a bunch of keys and coins.
Scratch it with a steel razor blade.
Drive a galvanized deck nail through it with a claw hammer.
Drill a hole through it with a SiC drill bit.
Heat it up with a propane torch.
Put it in a freezer.
Drop it from 2m onto a hard floor.
Bend it in multiple directions.
Pinch it until it cracks.
Try to find a resonance frequency with ultrasound.
Perhaps this one was more for optical properties? Refractive index, absorption spectra?