Not sure how you get A+B=C in your analogy. If C is distance to his face (literally just behind the magnifying glass), it can't be the sum total of the focus distance between the sensor and magnifying glass, and the magnifying glass to the hand.

Anyway, focus distance has no bearing on depth of field without knowing the aperture, since it'll have a far greater impact at T1.5 than at T16.

But if we assume they shot on 85mm, at T5.6-8, given how we can judge the hand in the foreground just out of focus, it would indicate that focus on the face/magnifying glass would leave the reflected image out of focus. On a long blend, you'd need deeper DoF to get both elements in focus. Thus, at our assumed 85mm T5.6/8, focusing on the reflected image will require further focal distance, which in the greatest of likelihoods will throw the face out of focus, not to mention the hand in the foreground. I've shot plenty of reflected images, you don't get the reflection, and the object within which they're reflected, into the same focal plane easily. I know this isn't a long distance, but we're still talking about a long lens, so this is highly improbable as you describe it.

Anyway; I agree about the lack of warping in the image that you mentioned; the reflection is too perfect, since magnifying glasses are convex on both sides and would cause a greater bulge in the middle of the image.