We don't Know something you don't. If you read further down the wiki page for easter egg it says
"While computer-related Easter eggs are often found in software, occasionally they exist in hardware or firmware of certain devices. On some home computers, the BIOS ROM contains Easter eggs."
It also states it could be music, pictures, messages, or hidden menus.
A hidden track inside the framework of a phones firmware seems to fit the description.
I think you have a too narrow definition of an Easter Egg :P
Doesn't have to be something big that's themed for the device (heck, come to think of it, Hover wasn't Windows 95 themed), just has to be something stupid funny that devs toss in :P Besides, if they named it so that it was obvious, it wouldn't be that well hidden, would it?