In Emulators / NES ROMs

I was browsing through my NES ROMs when I came across a rom called Mac OS demo.nes. I pressed all the NES buttons, but nothing seemed to happen. Anyone know anything about this? Here's a screenshot.

Quote from the :

"Here is a little demo for the NES (or an NES emulator) which shows a Macintosh "screen" on the NES. This is a good example of how to use CHR compression to get full-screen graphics. The older version of MacOS is also included in this archive."

The "older version of MacOS" he's talking about is another demo. It's not of much interest for "what it does". It's the "how it does it" that's of interest to programmers.