Look around, it's a damn fad. There is people collecting toys, watching the show every day, making fan art, converting others, dressing up like a pony, etc. You know what this whole thing reminds me of? This whole Pony fad reminds me of pokemon in 1998, this fad is so loving similar it's god damn creepy.
You're mistaking Fad and Fandom as the same thing.
Fads last a short amount of time with a large burst of popularity. The popularity of this show will continue to grow once season 2 is released as long as the show is still funny and appealing to us.
Sandvich gives exact definiton of fad.
Tony still says it's a fad even though it doesn't meet the definition's criteria.
That'd be like saying "This is a car" while it is a boat.
Then someone comes up and says "A boat doesn't have wheels"
Then the first person says again "No it's obvious it's still a car just look at it it's like that other car"