Sheet rejected for not having a 1:1 pixel ratio

[Witherskeleton]

Hello! I'm posting here because quite a few sheets of mine (all from the game Jimmy and the Pulsating Mass) were rejected for not having a 1:1 pixel ratio. Here's an example of one of them:

I'm confused because I ripped it the same way as the rest of the sheets I've ripped, but only this and a few other from the game have been rejected for that reason. I don't think there's anything about the game's images that is stored differently. How could I change this sheet to make it have a 1:1 pixel ratio? Thanks!

[Barack Obama]

- Open the sheet in your graphics program
- Reduce image size -> 50% of original size, filter: pixel

Some devs use a higher resolution for pixel art.
In this case, everything was doubled in size, which means every pixel is 4-times bigger (double the width, double the height).

[Witherskeleton]

Thanks!