I think you're probably correct.

I signed up and filled out two surveys (and was determined to be ineligible to respond to three). The surveys were claimed to take 5 and 15 minutes respectively, earning 50 and 60 miles. That also garnered the 250 miles introductory reward. They claim these take 4-6 weeks to hit my account. (Other surveys require 11 to 27 minutes to complete, and offer up to 120 miles for completion.)

This might be useful for someone with a lot of time or in need of some occasional activity to keep a generally dormant account from having accumulated miles expire.