Calzghe had the most unorthodox style in recent boxing history. He had great stamina and the ability to slap pitty-pat slaps non-stop. He beat so many because his style was so unorthodox his opponent couldn't figure out his style becasue probably no fighter in history had effectively used it.
Yer. He had great stamina either way but throwing a full power shot takes a lot more energy out of you.
He trained for that. He was a hard worker that put in the work, and conditioned himself to fight in a manner that allowed him to outwork his opponents.
I think his speed and punch output comes down to his punch style. He flurried with his palms, illegal in my book.
He ran a lot, 6 miles a day which incorporated 150m sprints and the area his gym is located is very hilly so most of the run would be up and down hills. This length and intensity of running probably helped a lot with his stamina and work rate.