No emp. We went over this in another thread.
Older computers would reasonably been programmed for altitudes up to 65535 feet, absurdly high for commercial aircraft. The U2 was higher, causing a “roll over”, subtracting that value until the result fit in range, placing the apparent altitude around 5-15,000 ft, right where other planes were operating. Result was the U2, flying high over other traffic, appeared about to collide.
Classic computer error, right up there with the Ariane 5 explosion (launched from a negative latitude, it computed impossible ballistic vectors, got confused, and blew itself up as a safety precaution) and Mars lander (confusing meters with feet, it followed a perfect landing trajectory and and shut off the retro rockets at the correct point - several miles up, subsequently crashing).
I HIGHLY doubt a 16-bit computer glitch caused this as many military aircraft have been tracked above 65535 feet for more than 5 decades. That, and many of the tracking computers are 21-bit.