Try to screenshot the tweet and then open it in an art application. The results are this: https://imgur.com/a/fyEJXtD
If you screenshot the image and put it in some sort of application like paint.net you can use some of the tools to see that there's actual difference in the pixel color. You can see this here: https://imgur.com/a/fyEJXtD
You can try it for yourself putting the image into a photoshop like application. I did it here and this was the result result: https://imgur.com/a/fyEJXtD