From the creator:

To better reproduce his style, make sure to add "norman rockwell style" in the positive prompt. Alternatively, you can try increasing the LoRA weight (1-2). If it has too much of an anime look, try adding "anime" in the negative prompt.

If you want the output to look more like a painting, you can add "painting" in the positive prompt, however, you may need to add something like "canvas, picture frame, paint brush" to the negative prompt. Alternatively you could use another LoRA with a more bold brushstroke style to coax it to look more painterly and avoid the word ambiguity.