Your English is not crappy, and is quite good for not being your first language!
Was this a different type of stone than you’ve worked with before? Did it have a lot of mica or quartz in it?
Did you have the material height (thickness) set correctly? (guessing you have to remove the crumb tray to fit the stone in and stay more than 1/2" (12.5mm) away from the head).
If the stone is not where the head is trying to measure focal length before a job and it tries autofocusing on the edge or even the bottom of the unit, this would confuse the GF, especially since the bottom is reflective–and any surface that is reflective is not good for the laser, and might be related to what has happened here.
Has it happened again with another stone, or other material with the same set up? One idea if it is due to reflection off the bottom, is place a dark sheet of paper or cloth on the bottom.
Did you watch the laser while it was running and see what order of the two 7s were etched? This might be useful for the problem solving. From the photo, it looks like it etched the “clone” first, and then the 7 in the position with the artwork (since the more solid area of it is over top the lighter clone). Not sure if the order is significant, but might help in the trouble shooting/problem solving.
Hope someone else with more experience with these materials or operating without the crumb tray can help figure this out.