It is only significant that something very specific and unlikely happens if you have specifically predicted it beforehand.
Here is an analogy. Imagine I am standing near a large wooden barn with an enormous machine gun. I place a blindfold over my eyes, and - laughing maniacally - I fire off many thousands of bullets into the side of the barn. I then drop the gun, walk over to the wall, examine it closely for some time, all over, pacing up and down: I find one spot where there are three bullet holes close to each other, and then I draw a target around them, announcing proudly that I am an excellent marksman.
You would, I think, disagree with both my methods and conclusions for that deduction. But this is what has happened in Lucia's case: prosecutors have found seven deaths, on one nurse's shifts, in one hospital, in one city, in one country, and then drawn a target around them. A very similar thing happened with the Sally Clark cot death case.