I too would be angry. I have had similar things happen during a theater install, once had a know-it-all who powered up and unfinished projection console and fried the lamp power supply. One $3,000 power supply and a repair bill from me for $900 and he got booted from the jobsite.
Nothing worse that someone who's "just trying to help" mucking about in your work.
I would also be worried about what else that person's "helped out" with.
