Awesome! Yeah, you would be surprised at how easily these plants can get pollinated. The pollen can easily travel miles and all it takes is 1 grain. It could have been self pollinated from a hermed bud site, or possibly got into your grow room from someone else's grow. That's the only downside of "bag seeds" as it's hard to tell exactly what pollinated and created that seed. It could be a feminized "copy" of the plant you're growing, or a completely different strain mixed with the strain you were growing. You'll probably figure that out once that seed gets to flowering stage! Good luck!