No Blast is still a mystery figure at this point, also in the manga, I believe. From the way they speak about Blast and Centichoro, it seems not 100% certain that it was Blast who beat Centichoro the first time – there are always some misreports or misunderstandings, like the ones involving King and Saitama.

Manga reader here, iirc Blast only show himself for a brief moment in the middle of the monster association arc, then at the end of the arc, this is still very early in that arc. Also they don’t really show how Blast beat Elder Centipede, just a glimps of it.