Yes this is correct. Those numbers are based on data published at http://www.newvem.com/topic/cloud-radar. For reference, light user are those with up to 8 instances, medium users have between 9 and 35 instances, and heavy users above 35. We didn't publish the total number of users in each segment, but I can confirm that that the survey was based on a sample of around 200 customers, as mentioned in GigaOm's article

The reason we chose to segment by number of instances is that we consider this as a good metric for the complexity of one's cloud footprint, and the corresponding effort required to manage this footprint.