think of it this way
"Darwin's theory is confirmed because we have more theories that confirm it"
:shrug:
The shrug indicates that you are neither familiar with some basic scientific terminology - nor have you fully understood what when on in this study - if you had you might have gained an insight into how science works.
I'll break it down for you:
What a theory (in the scientific sense) is:
an explanatory framework that explains a series of facts (remember this its important)
What a theory does:
Makes predictions that can be tested.
So what happened in this case was the scientists involved took one of the predictions made by evolutionary theory - namely that complex cellular structures evolved from simple cellular structures with often unrelated functions, and aksed a question:
"If this is true then we should be able to find them - where shall we look?"
They then hypothesised (NOT theorised) as to where they might be found based on a sound knowledge of cell biology and went looking.
They found what they were looking for and the results confirmed the prediction.
It is in fact a very neat illustration of how science works - prediction - hypothesis - test - result
So the theory was not confirmed by another theory as you so naively put it - the theory was instead reinforced (again) by (yet another) series of facts.
Conversely this doesnt bode well for creationism or ID (yeah ok - I know you're about as surprised as me by that one).
Creationism would predict that an omnipotent creator would create the optimum cell machinery from unique designs - which is clearly not the case here - cell machinery is neither optimum nor - as this study concludes - unique in origin.
ID's predictions of irreducible complexity (despite having been (quite literally) laughed out of court many years ago) - are similarly dead in the water.