So it looks like that 5GHz Wifi for something from Sony was confirmed to be for the PS4 Slim
http://m.neogaf.com/showthread.php?t=1270869
Unless specified otherwise.
So it just narrows that PSP-like device to either a Chinese Handheld Android device or supposedly the NX.
What reasons would this device be supposedly the NX?
-The worker probably saw a prototype model if it didn't have any branding on it.
- He assumed it was a Sony device because if he saw something with two screens, he probably would have identified it as a 3DS.
- If he knew what the Wii U Gamepad was since Wii U's are manufactured at Foxconn, he could have identified it as that.
So the speculation is: If it's the NX, it would have been smaller than a Wii U Gamepad.
However, it's just as likely that this PSP-like device is just a Chinese Android Handheld because there wasn't any funny description about the controllers since we assume them to be detachable.
So at this point, there's not much to go off of unless that Foxconn worker can leak more about it.
Edit: To misidentify something is possible. If you saw an unbranded Wii U Pro Controller with no details on what the buttons are. You'd think it was a new Xbox 360 controller if the Wii U hadn't been revealed yet.