Leftover tools and trash in work spaces is really common in the contracting industry (any of it). I install low voltage cabling and components for a living (networking, access control, cameras, etc) and I constantly find junk left behind from previous contractors. I was just in the plenum space of a building yesterday and found coke bottles, a beer can, and old paint brushes from a job that apparently was done back in 1994. The only reason I know that is because one of the workers bought a newspaper and left it there, too! The workers don't care. They know the owners are never going to go inside those spaces, and it's just extra work for them to clean it up afterwards. Thankfully, if you're intentional about cleaning up after yourself and being presentable, you can really make a name for yourself in any contracting industry.
I guarantee y'all have a coke bottle or something somewhere inside your house walls! Sad, but true.