it's true that the number of bitcoin wallet users is still very small, but I strongly believe that number will increase over time.
I think that survey is only came from the popular wallet or exchange how about the local wallet can use by the people in every country. That is only my own opinion.
popular wallet have lots of users compare to unpopular ones and local ones but 35 million users for one wallet brand is already alot , how much more if combine with all the wallets and exchanges ? that would be over billions or even trillions of users but not every single number is owned by a real and individual person because most of those are only dummy accounts or bots that are being used for mass farming in order to get referals so their main accounts can earn an incentive .