The strikes of the shorts are 50 points higher than the strikes of the longs.Yes, on the rally his gamma exposure shrinks as the market moves away from his long puts, but his deltas are always moving in his favor when short the calendar...just increasingly less in his favor as the market rallies away from those strikes. His long delta position on the rally may or may not have been enough to cover losses on the shrinking IV differential between the front and back month. That would depend on how wide the IV differential is between the two puts and also the vegas between the two puts. I'm also assuming the puts are same strike.
During the crash in March his gamma levels peaked as his OTM puts probably became ATMs or even ITMs, which would have left him a crap load of stock or index futures to buy near the bottom. I'm guessing he sold out of his winning put longs instead of buying the underlying against those puts near the bottom. If he wanted to keep the gamma he would have needed to delta hedge to lock in the big gains in his front-month puts. Most traders would have just launched the puts or option premium in another strike to lock in the huge gains. But keeping the gamma probably would have made you multiple times more money given that we were at one point having 10 to 15% ranges in the S&P 500 everyday.
