That comment shows such an infantile understanding of democracy. Having a single party simply means that Cuba decided on the approach how to do things, which is communism. There are lots of different approaches you can take towards achieving the goals within that scope.
Elections with one party have exact same purpose as elections with multiple parties. The citizens select candidates based on their ideas and proposals. The main difference in a multiparty system is that people still haven’t figured out what the right way to run the economy is, and each time a different party gets elected they pull things in a different direction. This is why it’s practically impossible to do any large scale projects in the west.