A single coil is bent at about 90* from norm. It looks like a crazy mess, but examine it carefully. This happened while the spring was compressed. No other way.
The spring was defective. Bad heat treat? Age? Damage? We'll never know.
When the spring was fully compressed, the coils did not stack up as normal but rather were forced either fore or aft in the mag at the weak spot. As the spring tension was released, the weak spot allowed the spring to gain some friction from the inside of the magazine which further promoted the spring losing proper shape. Didn't happen instantly, it was a process. If you had taken the spring out months ago, I bet it would not have looked straight, but rather had a bend at the 6th coil.
As the spring continued to lose strength at the weak spot, the other portions of the spring were still strong. The weak spot work hardened until instead of just not stacking up normally, that coil lost any ability to act as a spring at that point. The spring bound, got bent, and you see the result.