Sonic the Hedgehog 2 Metropolis Zone "4" found?

[Encoder [WantaPS]]

Well, I screwed around hoping to learn about ROM hacking in SonED, and I came across something weird......

A fourth Metropolis zone act.

Anyway, upon looking through the files, I saw the layouts as follows.

Metropolis Act 1 - Metropolis Act 1
Metropolis Act 2 - Metropolis Act 2
Metropolis Act 3 - Unused but complete level design.
Metropolis Act 4 - Metropolis act 3

Can anyone shine some light on this?

I don't know if it's the ROM I have or not...But Ive never heard anything about this.
Is this the first act of what could have been Genocide City Zone?
(^No pun, that's what it was going to be called. You know, to all 2 of you out there who don't know.)

[Encoder [WantaPS]]

As SonED has no Zoom function, Here's a picture of the fourth zone.

[Marble (LS5)]

Ohoo! I hope this is real!

[Encoder [WantaPS]]

Here's its location in the "Load your level" bar.