We had made no structures in the world, and had only explored for about 20 seconds before coming across this after some mountains.
I re-entered the same world seed again as shown in F3, and went to the coordinates, however it did not produce the same results, or even the correct biome. Try it for yourself, and see if it works. I promise you, I am not trolling, a legitimate portal spawned in the world.
EDIT: I just remembered something! When I put in the world seed, I actually used this 1.8 seed: -341414797482072298
It claimed it had a stronghold, so I looked for it.
EDIT 2: I used that world seed again, and went to the same coordinates, but found no portal. I am confused. It's possible that I copied the seed wrong, or it was a one-time glitch. I sincerely apologise if it was the first option.