Sheared off security Lug nut

Hey there, I was driving my Tacoma yesterday and started to feel a bit of a wobble, and a slight noise almost sounding like a flat tire. Pulled over, looked at all the tires, and one looked slightly low (not low enough to warrant a noise) so I stopped at a Gas station to fill it up. While checking my tire air pressure I felt the lug nuts to see if anything was loose, they all felt fine. When leaving the gas station about two miles down the road the noise and the shake got a lot worse. So I drove it home, and had it towed this morning, while it was being loaded on the truck I noticed the security lug nut on the driver side was sheared off, four lug nuts were loose (finger loose, could turn them all multiple threads in), and the sixth felt tight (I think the whole load of the wheel was sitting on this that is why it felt tight). It got towed to the dealership. So I'm wondering what could have caused this? I bought the truck about a month ago at 44,800 miles it is now at about 46,400. Before I purchased they did front brake work and a tire rotation. Any insight would be helpful, I would like to have a little bit of an idea what I'm talking about when I talk to the mechanic. Sorry, I don't have any pictures to show.

 

Somebody try to jack your wheels?

Possible they didn't torque the lug nuts to spec or tighten them down? Do you have the key to the security lug nut?

Pics?