Russian Topol missile test spotted from ISS

This matches. The missile has three stages (like the old Saturn V rockets that took humans to the Moon), and what the astronauts saw may have been a fuel dump from the second stage or the last of the fuel leaking away after the booster phase was complete. In space, the cloud would expand more or less freely, moving rapidly as it traveled along with the booster in its path. In the photo, you can see a slight streaking to the cloud, most likely due to motion.

via Russian Topol missile test spotted from ISS..

Original tweet from astronaut Mike Hopkins here.