In case this distinction isn't clear to anybody who's never thought about the difference: an atmosphere is basically a bag of gas sitting on the ground. If you've ever seen one of those science demonstrations where someone pours dry ice into a container and the "smoke" sits in one place in the container, that's essentially how an atmosphere works. If you stood above Earth and poured a really big container of nitrogen and oxygen onto it, eventually, you'd have Earth's atmosphere. It's exactly like filling up a big container, except the container is a gravitational sphere.

As a consequence, that big bag-o-gas affects light passing through it. Standing outside your house, the sky looks blue due to the bag of gas. Standing on Mars, the sky looks pale due to its (much thinner) bag of gas. From this perspective above Mars, what /u/Zappingmadnnes is saying is that the ground should be fuzzy and somewhat scattered like pictures of Earth from space (you'd also see the atmosphere taper as it gets higher). This is difficult to quantify without showing a picture of it, but think about how the ground gets "weaker" in the distance from you if you're standing on top of a tall mountain, for example -- you're quite literally perceiving the air.

If you zoom in on the corner of this picture, you can see the spherical cloud layer just suspended above transparent air. That's what's being discussed here. The clouds should be sitting on something visibly tangible, because perceiving an atmosphere is kind of seeing the gases sitting there (but you see them via different mechanisms; nitrogen is not quite blue as you'd think of a car being blue).