Quite a few people are "100% sure". I for one am and have already explained why the ribbon says that
here.
The way it works is that all ribbons in the game have the default "Mystery Zone" text untill something (in this case an event) tells the game what should be put there. If someone hacks a Clasic Ribbon onto a Pokemon without having the event "activate" it then the text will be the default one. So if that person then trades or battles with that Pokemon then their game will try to "correct" the others person's game to make it what it thinks is the correct text. If the event was legit then the correct text would be overwriten every time you trade or battle with it, but since it has the wrong text then the incorrect data would keep overwrighting other games thinking that they are wrong.
And to prove it, my ribbon's text hasn't changed once since I stopped trading with random people and only trade with people that I
know don't hack. I've traded for miltable English, Japanese and German events from them that have the Clasic Ribbon and it's stayed the same each time.
P.S. If anyone is familiar with Animal Crossing for DS, it works the same way as the hacked items in that. Except unlike with Animal Crossing, there is a chance to get the data back to normal instead of having the slot used up forever.
