No. It really is possible.
OK so he's probably seeing a skin coloured blur AND a red blur.
Take off my glasses and my clear vision extends to just past the tip of my nose. At roughly the distance in the drawing Lily is definitely far enough away to be blurry.
Further away and she would probably be just a red blur.
No, my glasses aren't that thick. Admittedly, forty years ago they would have been, but that's when we wave our wands and say 'magic' (just like the fact that Harry apparently never goes to the opticians in seven years and his prescription stays exactly the same)