On the subject of naming, the proposed term of art in C++ is Uniform Random Bit Generator (URBG):
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0346r1.pdf
The original terms were uniform random number generator (e.g. Mersenne Twister) and random number distribution (e.g. Uniform, Bernoulli, Poisson):
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3551.pdf
The proposed renaming was to make it clear that a generator shouldn't be used as if it were a distribution. Maybe the Swift APIs don't have this issue.