IMO, not surprising at all. Note that he wasn't some random couch potato, but someone who had already been putting in the work of getting into good shape for (

IMO, not surprising at all. Note that he wasn't some random couch potato, but someone who had already been putting in the work of getting into good shape for (at least) two years prior according to the article. So for this guy, he was "just" adding a high-intensity subcycle to his existing training, a cycle which his body was able to adapt to. This is hardly an unusual pattern for those doing serious strength training.