SAI is steering axis inclination. This is the steering angle and geometry engineered into the suspension and steering by the car's designers. The tech is correct in saying that if it can not be set then a part is bent. SAI is not adjustable and can only be restored by replacing bent or broken parts.
The rear may be cocked or experiencing a 'dog track' situation where the rear is not square to the chassis because of bent or broken parts. You see that in trucks and vans when their springs are shot from carrying heavy loads all the time. if you drove it with this condition, you will have to compensate with the steering wheel to keep it straight. If you looked at the car from the roof and a drew a line from stem to stern, the rear wheel track line would eventually intersect the centerline, which is what he means when he says it's cocked. This can also usually only be repaired by fixing bent or broken parts.
Sounds like you smacked the curb pretty hard. Good luck.
