User blog comment:Halo1081/Chapter 128 and forward/@comment-25886825-20150304234415/@comment-4911196-20150305130319

Yep, it confirms it. Korosensei was also a human as well before he was turned into one of test subjects which turns him to what he looks like now. Class E is evidently not a coincidence as he know Class E kunugigaoka is the class where Yukimura Akari, the person who oversee him at research facility teaches Class E.