Could be a bit of both. Did you use an impact driver to tighten the wheel bolts? If so, make sure you aren’t using one that’s too powerful. And don’t let it hammer onto the bolt too much.
Otherwise, its not totally unusual for studs to break when they get older.
I consider them to be a wear item. I replace them at a minimum once per year. Usually the threads are damaged from running the nuts on with an impact. In a perfect world we would only do these by hand…