Agree that muscle gain is putting in the work, but the same can be said for most sports. The reason it's relatively impressive the stark contrast between how emaciated he looked as a runner and that he now looks likes someone the average person on the street would likely consider "jacked". He's nowhere near becoming a bodybuilder, but he does look pretty good.
I guess most men under 50 can make "huge gains" in under three months, if that means going from completely untrained. But then, those new gains are going to slow dramatically. Ryan Hall has clearly put in years of work for his physique. Sorry Flagpole, he is a far more accomplished runner than you, and now he is way more jacked than you too. It's okay to admit your jealousy.