I think, it's like, he's not a fan of that specific type of artwork, but he knows you worked really hard on it. It's like if someone doesn't like the art style of Mob Psycho 100, but they know that whoever animates it spends so much time working on it, trying to make it look good, and other people like it. Besides, he's not saying that he likes the art, just that you did a good job on it.
