mean.rv gives the distribution (that is, a random variable object)
of the statistic $\frac{1}{n}\sum_{i=1}^n x_i$
(sum(x)/length(x)). In particular, mean(x) of a random vector x of length one
is equal to x as it would be in the case of numerical x.
To find the expectation of a random vector x
(that is, the individual means of random components in a vector),
use rvmean(x) (same as E(x) and Pr(x).