Alright, let's see what this Thunderthief thing is about...
Right off the bat, we have the name. Thunderthief isn't an amazingly accurate description of what it does, but that's okay. We don't refer to everything with a perfect description, and Thunderthief does sound like a reasonable name someone would come up with for these creatures.
The type is Aberration, I noticed a few people saying they think that this was an attempt to dodge the "No Outsiders" restriction, but according to the Pathfinder SRD, "An aberration has a bizarre anatomy, strange abilities, an alien mindset, or any combination of the three." Let's see, their gullets are larger on the inside than the outside. I'm fairly certain that a stomach which bends the laws of the universe counts as bizarre anatomy. Likewise, thunderdash is a strange ability (at least in my eyes), so I think Aberration is a fitting type.
The statblock itself doesn't cause much alarm, with the exception of the DC for the aura. The Aura seems a bit harsh, but I'd want to see it in action before I passed a final judgment on it.
I admit to not knowing much about Golarion, but I don't understand the fuss concerning the Environment being a specific place. I mean, I do understand part of it, you want a monster to be accessible and some DMs might look at that and say, "Well, I guess I won't use this monster after all." But, honestly, if most DMs want to use the Thunderthief it will be because they think the monster will make a good fit for their game and not because they read the setting book and said, "Oh my goodness! I need to run a game in the Eye of Abendego right now!" And if a DM likes a monster and puts it somewhere contrary to its Environment listed in the statblock, that's fine. And the first player who says, "The book says they're only encountered in X spot!" should be smacked upside the head.
I recommend that you vote for this entry because it's an interesting monster, just don't get caught up in the wrong minor details and let those ruin it for you.