The dependency resolution of PKGBUILDs which depend on parts of a project which may be provided by multiple packages are handled differently at the official package browser than it is done in the AUR web interface.
For example the package gnome-session [1] depends on libgl, however libgl is provided by both nvidia-libgl as well as by mesa-libgl. On the package browser at the archlinux.org page all of those alternatives are shown in brackets. However the AUR web interface is unable to resolve those connections (see [2]).

[1] https://www.archlinux.org/packages/extra/x86_64/gnome-session/
[2] https://aur.archlinux.org/packages/zoom/