Yeah that is sand. I can take similar photographs that lead you to believe there is water ( or many other things) when the truth is quite boring.

And that is the ticket isn't it?
To those of us that this stuff is unfamiliar- we think we found something. We get all excited.
I'm glad I don't pay Hoaglands underwear bill.

But to the folks at NASA, its all quite humdrum and routine. They were all over this picture, recognized what it showed with a practised eye and went on to the next.
They don't always think about how the common person will react to seeing it.
The common person doesn't always think about the experienced guys at NASA yawning at such photos- of the likes they have seen so many they have dreams about looking at photos...

The reason most people don't understand the motivations of the teams at NASA is because... they don't work there. They don't diddle over this stuff every day, day in day out, with a lot of knowledge about the lighting, landscapes, weird conditions and photo-taken-then bundled-transmitted-recieved -and interpretted that most people not in that line of work aren't aware of.
Run on sentence. Remember to breathe as you read it.