That absolutely sucks. I am sorry this happened to this person.
I can't help but wonder that his last theory is the most accurate - they were moving things around looking for valuables and accidentally made the shelf to fall, busting a lot of equipment in the process. My reasoning is that, if someone wanted to really trash the place, they would have beaten and cracked the LCD screens, shattered the nice framed picture on the wall, thrown the 3D printers around, etc.
Well, that or they were spooked by something and couldn't finish the job.