Drilling a lug bold should not be so, lug bolds are not very hard.
It took me 5 minutes to drill a broken bold out. The trick is low revs and great pressure (and a sharp drill!).
Because they are not very hard they stretch every time a little bit when they are installed. Especially when they are overtorqued, as most tyre shops do.
When my bold broke a inspected bolds, they were all worn and had to be replaced. I was glad to find this with a tyre change and not when I had a flat.

If they all break they are very much overtorqued or completely worn, either way the guy who did this is incompetent