Yeah, he was, but it's still a different sort of thing. Ars Arcana describes the surge of Illumination as being "closest to the original Yolish variant", so they definitely differ fundamentally somewhere to only be "close".
I think painters and people who sketch and draw should be distinguished despite both fabricating images of things, no? We probably shouldn't lump all illusionists together even if they have the same name. It's about as fair as calling Seons and Spren collectively as just "Splinters" disregarding differences.