Yep looks like that stud is broken off. I believe it is welded in in the wheel well like you said, but luckily you can get access to it. It's kind of hack, but the easiest solution might be to chop it off with a cutoff wheel and knock it out, replacing with a bolt/nut from the hardware store. Since our cars only have the 3 mounts, it's pretty vital that they be attached well.
