ok. the first red flag is the fact you're in creative mode.
based on what I see in the pictures I'm assuming you build structures in that minecraft world so you could have just made this after you finished one of your builds.
you were very sloppy about faking it to. if you look closely in the first picture you can see there is a dirt block next to the portal which means that when the portal was made you misplaced a block and turned a grass block into dirt.
you can also tell that both screenshots are in different places. you can tell by looking at the left side in the first picture. in the bottom left of the first picture you can see a grass block. that grass block is absent in the second shot.
also in the first shot you can see there is sand a few blocks past the portal so in the second shot we would be able to see the sand.
and if you look closely you can see a lot of the landscape has changed.
also who would have made the portal? who? even if it was herobrine or entity 303 or something it's unlikely they would make such a strange nether portal.
you also cut off your hot bar in the second shot which makes me think you took the screen shot not realizing there were materials in your inventory.
