In the Creating a rustup toolchain section, here is a part:

... The first
one will run the stage1 compiler (which we built above). The second
will execute the stage2 compiler (which we did not build, but which
you will likely need to build at some point; for example, if you want
to run the entire test suite).

rustup toolchain link stage0 build/host/stage0-sysroot # beta compiler + stage0 std
rustup toolchain link stage1 build/host/stage1
rustup toolchain link stage2 build/host/stage2

It says the first and the second to (probably) mention the second and third item in this list; it is confusing.