We know how cells replicate and differentiate. We know that limbs do not spontaneously and immediately regenerate.
Well... that's what we
used to know... until we saw a limb regrow instantaneously before our eyes.
It wouldn't just be something we don't know about yet, it would be something we know enough about to know that it couldn't possibly happen.
Except that it happened. So obviously something's wrong with our understanding of the way the world works if it rules as impossible those things which clearly take place.
But why worry about only limbs. Let's have a man with a severed head walk around normally for a month - or anything else you can think of that we KNOW is impossible.
Why not revise our scientific theories to account for the new observations?
Love your enemies!