When I saw Piglet not backing up under his tower I was thinking "Oh its just 1 of them, why are they teleporting a free kill right to mid lane? Well he can just net out if he.. OH GOD ITS TWO OF THEM" At the level I play in, we don't actually see a lot of dual TPs, let alone dual TP plays so its kind of expected I'd fall for it, but Piglet scrims against these kind of scenarios all the time, you'd think he would have some experience to fall back on for this sort of thing.
You're right, he plain and simple didn't respect the 2 TPs, not to mention net would absolutely not have saved him from Ryze. He was asking for trouble and got it, sadly.
I mean if you're the ADC alone in mid and somebody starts channeling a TP right in front of you, that's some juicy bait. Your spidey senses should be going off full blast and all the Admiral Akbar memes on the planet wouldn't have enough "ITS A TRAP" to fill the need this situation creates.