We do?
That assumes rather much, as none of the artists who created those images ever laid eyes on him, and the shroud has no particular validity.
How did the artist create the image on the Shroud of Turin? The hundreds of scientists who have studied the Shroud for years would like to know.
How do we know if the earliest icons/paintings of Christ were not written/painted by those who saw Him in the flesh?
In any event, it is not of primary concern. The Bishop's clarification did a good job in describing what is of primary importance to us.
The greatest miracle for us is the Eucharist itself! Anywhere it is offered. That there have been times in history where our Lord has chosen to show forth secondary miracles in union with this great Sacrament/Mystery to help deepen or strengthen Faith (or whatever else for a reason) in It, is His call. These miracles could even follow upon natural causes.
It is not within the normal course of events for the pattern of a face to become present in an exposed Host. Since this occurred here, and since the image seems to match up with images recognized by Christians as that of Christ, then it is not necessarily a mindless step in the dark to suppose that the Author of this (purported) secondary miracle meant for it to be understood as an image of Him confirming His Real Presense in the Eucharist. Either as a reward for the Faithful adoring Him there, or to strengthen their Faith, etc.
Do recognize that even the Bishop invited others to issue explanations for this event that would involve natural phenomena/causes. If you have any, I'm sure he would be delighted hearing from you as it would aid in his investigation in determining whether or not this is truly a supernatural miracle worthy of belief. I gathered from the article that he hasn't done that yet.