14.4% of Americans seems awfully high to me. I wouldn't be surprised if the results are skewed because the respondents weren't representative of the population. Some demographics will definitely have a higher propensity to use Bitcoin -- Millennials, internet users, etc.
A lot of people might have created Bitcoin wallets for fun (it takes just a few seconds). But these wallets are all empty, with no transaction ever occurring with them. I am afraid that the survey might have counted these wallets as well. If you ask me, I would say that 14.4% looks possible within the 15-29 age group, but not among the general population. Ideally, we should only count those individuals who hold more than
BTC0.001 in their wallets, or those who at some point of time had that much BTC in their wallets.