Here is a bit more background on what they see now vs. a time frame from long ago:

This is potentially actual water, in the liquid state, flowing on Mars today not millions of years ago. In late spring and into the summer is when these features form and fade. By late summer – early fall they’ll be completely gone and we’ll see just a normal looking slope throughout the winter.

Commenter Mat had this to say:

Water cannot exsist in liquid state on mars due to low atmospheric preasure

Who knows for sure?  We will likely know more in the near future as NASA gets more data and pics. We hope you like the video!