Interesting choice to have people sign up for free stickers. I expect a follow-up article on "The Marketing Behind the Marketing Behind MongoDB" :)
Etsy did a three-part series on the benefits of MongoDB in the early 2010s.
MongoDB was also well known for its stickers, and their marketing team wrote online about how these stickers helped solicit emails:
"Give away swag: This is a low cost, easy way to build a lead database and get developers to decorate their laptops with your logo!"
This is like the kale salad of that type of marketing. It is definitely effective, though.