Wow! That's not good... Ember from a campfire that got in there when you were closing it last? Or maybe a chemical reaction with something like bug spray? Yikes! :Wow1:
My guess is your thinkin' is along the wrong lines. That is not melted from heat but chemicals. Betcha there was something on the tent that the nylon in the screen didn't like but the nylon in the tent (guessing they are not the same) ignored.
I am going with... it was their from your last trip and you missed it until now.
But it's a good possibility that... you have a rat who likes loose change and has a nasty habit...
Just keep an open mind.
Does the area around the burn smell of chemicals?
Bummer either way.