Container Labels
Each of these labels in the table is stored as metadata inside the container, available at /.singularity/labels.json. The labels carry a URI specific to either Singularity Hub or related applications like this one (Singularity), Docker (DOCKER) or without a label means it was derived with the bootstrap. If you see a label that begins with SINGULARITY_RUNSCRIPT_ARG_*, this means it gets parsed as an available argument for this application. More information is available in the README on github.
Container Input Arguments
The container input arguments are derived from the labels, and the type is determined by the ending term of SINGULARITY_RUNSCRIPT_ARG_*