I suspect this is pretty conventional, a bomb threat from a disgruntled employee, or maybe some wacko convinced the observatory is a refueling base for Deep State black helicopters.
I also understand that observatories are frequently the targets of environmental crackpots and religious fanatics who feel that endangered species or sacred sites are threatened.

Referring to your sidebar about shooting out the big reflector's mirror, I remember reading about that. As it turns out, a bullet will gouge out a piece of glass from the mirror, but will usually not crack the glass, affecting a larger area. Since the figure, or paraboloid curve of the reflecting surface, is still intact, the only repair that needs to be made is to paint the chipped-out bullet crater with flat black paint to suppress stray reflections. The only effect on optical performance is a tiny reduction (area of chip/area of mirror)in the brightness of the image, the resolution or sharpness is not affected at all. Remember, in a big reflector, there are already many obstructions (such as the secondary mirror and its supporting struts) suspended in the light path.

A similar issue occurs in large refractors. The molten glass used in making large lenses unavoidably forms tiny bubbles at the foundry. These bubbles are trapped in the glass as it cools, but they do not affect the image quality because they are out of focus at the focal plane. Likewise, the dust and atmospheric pollutants that fall on the glass are only cleaned off infrequently because of the potential of damaging the figure of the lens. The image brightness is affected only negligibly by these obstructions, and the image sharpness and resolution not at all.