No...no...no...You have it wrong.
The connection of purple and portal has nothing to do with the set. What you're probably remembering is an old issue of InQuest where they made a dream card set that revolved around their idea of what Purple should be. Sadly enough, the "basic land" for this sixth color wasn't a land at all, but "Portal."
So in their retarded minds it made sense that if you have...
Mountain, Swamp, Plains, Forest, Island...
...you should add PORTAL as the next logical choice! Yeah, no wonder they get teased a lot.