It's the armchair experts asserting that, even though it's clearly not one, that it is.  And all the wishing in the world doesn't make it so.  By that rationale, I say it's a tuna.  I want to believe!

 
With proper reading comprehension you would notice that I said it "looks like" a tiger. The definitive statement came from you, the (bona fide?) expert who ruled it out completely.
 
All anyone can really do is make an educated guess.
 
The main identifying mark of tiger trout is the vermiculated pattern, in a greater or lesser degree, which is typically a characteristic of brook trout as any ID guide will tell you. The presence of tiger trout in PA and the broad range of color variance that they can exhibit is what I based my guess on. I could of course be wrong.
 
There is polymorphism in brown trout leading to different patterns and such. Plus plenty of species (or not, the verdict is still out in some cases) that look quite similar.
 
The confusion over trout in the Balkans shows once again that correct identification purely by eyeball when it comes to hybrids and morphs can be next to impossible.
 

 
"The Balkan Peninsula is home to the most diverse collection of salmonids in the world. Nevertheless, many taxonomic uncertainties remain unresolved despite over a century of studies." - http://balkantrout.blogsp...other-myth-busted.html
 
"Adding to the confusion of salmonid taxonomy, there are other trout with marble pattern beside Salmo marmoratus. One is trout from the river Otra, Norway. A certain percentage of brown trout (Salmo trutta) from that river has marble pattern. In all other aspects, these trout are identical to the non-marble brown trout from the same river. This is an example of intrapopulational polymorphism." - http://en.wikipedia.org/wiki/Marble_trout
 
(Those Otra River browns look a lot like tigers, causing some to call them "the strangest brown trout.")
 
These are the kinds of places the browns in PA trace their roots to, since Europe is the species's home range.
 
Things get even more complicated when you involve breeding programs with fish and eggs from different sources, the shipment and stocking of fish, introducing species, a lack of studies, etc.
 
Anyway, that's about all the conjuncture I have time for.
 
Here's a picture of a big tiger from the Loyalhanna DHALO section that I found (thanks Google Image Search!) to part on. Enjoy!