Spawner obtained in minecraft survival with no cheats?

I found an abandoned mineshaft and there was a cave spider spawner, a creeper was next to it and blew up, blowingbup the spawner and making the gravel above falling, with water pouring in from a nearby water cave of some sorts. A while later i checked my inventory for some food and i saw that i had a monster spawner in my inventory, and i didnt have cheats enabled on that world.