It was all over national news, and some international news, for days.
You might not be sure, but you don’t have to be sure. I would expect they got a very large number of tips, most which did not pan out, of course.
But I also don’t think it’s ever been confirmed that it was an employee. My suspicion is there happened to be some law enforcement officer and they called it in. That would explain the rapid response, and the caginess about the tipoff.
For a $50k reward? Yeah, I don’t know what McDonald’s employees make at that location, but it’s probably low enough to make that very tempting.