2 of 2 Minor format adjustments. Image size reduction (px and kb).

Do you have another Android device (like a phone, maybe) that you'd previously connected to that same Wi-Fi point?

Android 4, Ice Cream Sandwich, (and possibly older versions too, though I don't have any to hand to check) has an option to sync saved Wi-Fi passwords between different Android devices on the same Google account. Here's the option under Settings -> Backup & Reset on my phone:

ICS Backup & Reset settings screen

There are also apps that allow you to sync Wi-Fi passwords between your laptop and your Android devices, though I assume you'd know if you had one of those installed.