First I thought he was working around a broken wire. Except he did it twice.
He just believes paralleling wires is a good idea. He's wrong.
Each wire provides a separate function, and each is important. But paralleling is bad even if you had an extra wire, for other reasons.
For each cable he surely did the same thing with both ends. So that means you need to follow those two cables upstream and downstream (to the lamp) and inspect there too.
All this needs to be corrected. If the house is full of it, it'll be a lot of work. You can do it if you're willing to get a book at the library and school up on wiring basics. (don't learn too little and end up making it worse, that's what he did!). You can hire an electrician but it's big dollars for not terribly hard work.
Since you can't fix the whole house at once, work with one cable at a time, and correct both ends of the same cable. If you can't clearly identify which cable is which, then do one circuit at a time, fix all its cables. You can tell what's on the same circuit because it lights up when the breaker is on, and turns off when the breaker is off.
In the meantime, this is a serious wiring hazard for so many reasons. I would at the least get some GFCI + AFCI breakers until it is fixed.