How to check Drupal distribution version from CLI?
Just run the following command from the root directory of your Open Atrium installation:

drush status-report


This should give you the output similar to the status report screen in the standard Drupal backend. In my Open Atrium installation, one of the lines reads:

Install profile            Info      OpenAtrium (openatrium-7.x-2.18)


So in this case I'm running Open Atrium version 2.18.