So most likely the valve clearance was adjusted inappropriately by the previous tenant, and you've now put it right so all should be good.
One of my tedious stories: years ago my sister's then-boyfriend asked to borrow the workshop manual for a car. Knowing he didn't even own a screwdriver, let alone a car, I asked him why he needed it. He said he and his mate had decided to replace the breaker points in the mate's car, and now it wouldn't start. I asked him what gap he had set them for. He said, "Gap? What's a gap?" It seems they'd just slung in the points and done up the screws, job finished.
Sounds as if your whippersnipper owner's mate did something similar here: "Ah, I can see the problem, these rocker arms are loose, I'll fix that for a start." Most of us do that kind of thing when we first start out, and learn by doing. In this case it did no harm whatsoever, and you can be pretty sure there is one person who will never make that mistake again.
I'll close this thread.
