A perfectly healthy plant would not look like that. But, it is unusual for plants to be "perfectly" healthy.
I think that you might have potato leafhopper damage/burn.
Potato Leafhoppers from University of New Hampshire Extension
I'm going to forward your question to an entomologist for a second opinion. Look at the underside of the leaves on your potato plants and see if you can find any leafhoppers or their skins.
Yes, that looks like "hopper burn" to me.