This means that the OCS molecule soon comes to rest. Also, the helium-4 atoms immediately adjacent to the OCS molecule are localized by the strong chemical forces and rotate with the molecule. This means its quantum phase maintains a constant value over long distances. This is an unnecessarily narrow definition because it denies the possibility of superfluidity in a finite system like the helium-4 droplet. An analogy to a crystal will help the reader to understand this issue.
Textbooks define a crystal as an infinite number of atoms precisely lined up.
This definition works for very small systems. What is fascinating about this experiment is the juxtaposition of chemistry with superfluidity. On the one hand, it is a new environment for studying molecules. On the other hand, the molecules can probe for superfluidity. For example, an open question is whether vortices can exist in these small droplets.