Laser light is absorbed uniformly throughout the glass wall, producing uniform heating and avoiding thermal shock. The laser can also be controlled to produce gradual cooling to avoid any residual stresses. Residual stress can be checked by dipping the glass into oil with a similar refractive index, and passing light through the them under a polarizer. Stress will appear as bright zones, while a stress-free region will be transparent.
It’s very hard to get stress free regions around the edge where the glass has bent over itself to help create the seal;
FYI the shots above are of a stress loaded glass seal, not an ideal seal… but still, those points around the edge are the hardest parts to get stress free, and this is exactly where the glass is snapping off (as you posted);
It’s also why the break is basically perfect.