How did I know the pitch of Snake Rattle n Roll?

I fired up the NES game Snake Rattle n Roll today... but before I did, I was humming the themesong. The funny thing is that next door, the neighbor is playing music with heavy bass (Mariachi). And though the tonic was poured over me through the wall, I heard the theme song to Snake Rattle n Roll in my head... and it was in a different key. So I tuned out the next-door music and strongly hummed the game themesong to myself as I fired up the emulator... and... spot-on! Exactly right! Now this game came out in 1989. That's 17 years ago. Aside from playing it once when I downloaded it (probably a year ago), I haven't heard this song in over a decade.
That's close enough to "perfect pitch" for me.