I concur with Fudoh. In the screenshot shown here above, the border between blue and black pixels (wall / water) is sharply defined, but green / brown pixels are partly blended together, with a central portion looking like the original, while the border areas look horribly blended. This appears systematic, but how can we be sure of the cause?
RetroN 5 isn't supposed to output a 500x441 resolution so the result of that scaling problem could have multiple causes. Compare with the non sequitur captions in this Hyperkin advertising image:

Maybe this image appears in a context that explains what it's meant to show (I grabbed it off
this page without bothering to read what they wrote about it, and at a glance that looks like a justified time-saving measure), but it does appear that they are showing "idealized" (or worst-case, if that SNES 'screenshot' is any indication) images rather than images as displayed at HD resolutions, which could make some images look better or worse than others. It doesn't seem especially useful or honest.
What seems possible is that some of the images are being screwed up by image scaling after the fact, for publishing on the web. The Tumblr page is almost silent on detail about what the screens are meant to show, or if they even are meant to. The scanlined image is really bad, perhaps because it's been rescaled - as far as I can tell the scanlines look like they start at the right spot on each row (nevermind I don't think they should look anything like that, which appears to be a simple second-line-dimmed pattern), but the screenshot looks bad partly because the pattern results in a sort of vertical jailbar effect. Page 2 of
this document shows examples of a spurious bar pattern appearing due to scaling (bicubic and bilinear in the examples), just like those seen in the scanlined screenshot. It also shows a couple example of nearest-neighbor scaling problems and (the main thrust of the paper) a method of obscuring the spurious macro patterns it can generate, like what Fudoh mentions here.
I will leave you with some words of wisdom from the linked Hyperkin page to ponder deeply:
What interpolation does is instead of repeating each low quality sample, it creates new samples between the originals. As a result, it creates a smoother, crisper sound output than the original sound.
What kind of interpolation? Smoother AND crisper? Is crisper aliased? Who knows.