I think the art changed, or just his design

I don't think the art changed per se, nor did his design. It's more of a him being drawn with sharper (and maybe slightly bolder) lines/features in this chapter imo, I noticed that too

Well, almost every manhwa/manhua change and improve their art style as the chapters go on. So yeah, it's a little bit different

Art is the same, artist just evolved. Drawing is all about the brain and how you see things, it's natural for the style to change overtime, especially when you draw a lot.