Short answer: move the app out of the Downloads folder
Long answer:
In testing, I see this is happening if you run the app form the Downloads folder. The OS keeps track of downloaded binaries and auto-sandboxes them, apparently, by opening them within a temporary image somwhere. When Pd starts up, sys_libdir is set using the current working directory and picks up this temp location. sys_libdir is then used to generate the paths in the About file. When you move the .app somewhere else, this sandboxing no longer happens and the About paths look correct.