I contacted that guy and asked him about it and this is the reply I got:
"I had been doing some research and assumed that my copy came with a Disney Adventures Magazine because I used to buy them as a child, however another eBay member emailed me and informed me that he has that Disney Magazine and the comic was simply reprinted in the magazine, not inserted as a stand alone comic.
These must have been sold separately for the $1.50 cover price. It predates my comic book collecting years so I don't know why I would've bought it, maybe they sold it at Toys R Us or something like that and I convinced my parents to buy it for me, or someone else bought it for me and it managed to survive all these years. I don't clearly remember because I was only 6 at the time. Hope that helps."
So yeah, there you go...
I also contacted another guy selling a copy of DA because of the sonic stuff and he said that the story is printed within the magazine, but it's printed on a heavier weight of paper.