So in other Julia geometry-related projects that may be true, but for this particular corner of the ecosystem the main author (Júlio Hoffimann) has actually implemented much of the underlying geometry and other code from scratch (to the best of my understanding) in pure Julia in a whole set of packages, including e.g.

https://github.com/JuliaGeometry/Meshes.jl https://github.com/JuliaGeometry/Rotations.jl https://github.com/JuliaEarth/GeoStatsBase.jl https://github.com/JuliaEarth/PointPatterns.jl