To be slightly more clear, it looks like they're saying that there are two _types_ of neurons, not two physical neuronal cells. From the article's introduction

To be slightly more clear, it looks like they're saying that there are two _types_ of neurons, not two physical neuronal cells. From the article's introduction: "We demonstrate that the core decision-making system consists of just two neuron types—a phasically firing command-like excitatory neuron, encoding the presence of food, and a tonically firing modulatory neuron, acting as a gain controller for the animal’s motivational state—and we characterize these two pathways and their interactions at the point that a decision is made."