It's been a while since I took statistics, but yes, I guess that is a binomial distribution. It does not influence the results in the way you are implying it does, though. The calculator does actually account for it (the Population Proportion input), and the sample size actually decreases the lower/higher your proportion is. My point was that a question like, "Do you watch anime weekly," is not like a question like, "How many hours of anime do you watch in a week," where you certainly couldn't assume a normal distribution for the number of hours watched.