"getModelSubSystems" returns all the Subsystems exist in a model.
"findSubSysGen" is a special case of "findSubSystemsFromGenes" where it considers all the genes in a model and returns only one subsystem for each gene.
To get the your desired result, I recommend using the following line:
>>[~,singleList] = findSubSystemsFromGenes(model)
The first column of "singleList" represents the genes and the corresponding cells in the second column represents all the associated subsystems.