>>537722212
It was Goku. I think the only times Piccolo saw Vegeta spamming ki blasts were both times it was used on Cell, but Piccolo didn't comment on them.

Ironically, Buu copied "Vegeta's technique", but Vegeta never used it at any point during their fight (Or used it at all before fighting Kid Buu IIRC). I'm not sure if Vegeta used it on the anime either.