I think it is Go style to name things that come in as interfaces with short names. When you have an io.Writer, there's very little else you can name it other than "w" that would have any additional meaning or utility. When you have a variable or struct field of a concrete type, it can and should have a meaningful name, even in Go.
Ironically, I see several "input io.Reader" sort of things in that code, where as "number of hash functions" is k. A few minutes with go-rename would clean that right up, though.
The abstractions are supposed to be self explanatory and simple and thus the variable names do not have to serve as documentation.