So I am on the way to work this a.m. And this 18 wheeler decides to turn left all of a sudden. All is clear on the right so I drop into 2nd, turn the wheel right to change lanes then I let the clutch out and BOOM!

Something popped and car just revs-no go. I had enough momentum to glide into the parking lot and call for my coworker to pick me up. I tried all of the gears in the aprking lot and motor just spins. There is a little gear spline type grinding.
Is it a coincidence that I had the car inb the shop three weeks ago to have the Catalytic converter replaced? ($1500 warranty) Is there a possibility that they forgot to replce something when they put in the new exhaust manifolds? Does/is the tranny messed with when replacing converter or mainfolds?
What do you all think?