Keep reading. It's surely open source, but the license is mixed due to reuse of previous work that was CC-By 3.0 and similar.

An R package that I did was blocked from CRAN solely because they wanted me to choose a license from a fixed menu and I legally could not. Such policy creates a perverse incentive to not acknowledge previous work or to rationalize about the point at which the code is so mutated that it is no longer derivative.