Colum

because you are not asked to estimate the accuracy of the MEAN. In this case, the point estimate (sample mean) is virtually true mean because of the sample size. More technically, standard error = s/square (1000) ~0. Remember standard error is used for estimating the accuracy of point estimate as a representative of the true mean.
You are asked to estimate the minimum value to where 95% of population will exceed. As I said earlier, you can assume that the sample distribution represents true population and continue from there, since you are asked to
Hope it clarifies.