Depends on what sort of commands it supports, how well it needs to handle background noise, and how advanced their on-device voice recognition tech is.
For a company like Samsung, yes they very well may need internet access to do voice recognition at an acceptable level of quality. It's worth noting that both Amazon Alexa and Google Home also implement their voice assistant features that way. Google did recently move to on-device voice recognition on phones in the newest version of Android, but that was only possible to do without sacrificing quality thanks to some new advances in their machine learning tech.