First drive after brake upgrade, then - BANG!

If that is the T bar sticking out, it`s broke. It should not be sticking out, a big clip keeps it in.
IMO,
Looks to me that's in front of the trans crossmember and the boot is pulled away. Also, the trans crossmember bolt appears loose.
If the bar is broken, I would think he could shake it around.
If the bar height adjuster bolt stripped, the bolt head will likely be much lower than the opposite side. OP, don't adjust these with the car weight on them.

My '66 Charged bar snapped way back, sounded like a M-80 under the car. Front right dropped to the bump stop in half a heartbeat. Right turns on the way home chewed on the tire a bit.