I just did a quick check on these two screenshots. The files appear to be .png (which is the default and lossless format for screenshots), but one of them is actually a .webp, and the other one has heavy compression artifacts, which could mean two things: these images could have been uploaded somewhere and that website has compressed them, and later converted to .png again, or the source has used a photo editor software and saved them in multiple formats before exporting the final version. It's very interesting, as you can see in the attached gif, how the Android UI moves from one screenshot to another. This can be a weird Android bug or, more likely, suggest heavy editing on the screenshots.