There is no set standard for what can be considered a “hospital-grade” breast pump, and manufacturers often use the term for marketing purposes (source). This phrase doesn’t reflect how powerful or efficient the pump is.
People who have breast pumps marketed as hospital-grade are split over whether or not they are any more effective than other pumps.
The closest thing to a definition of hospital grade is that these pumps are considered, by the manufacturers, to be suitable for multiple people. In that case, the Spectra S2 is not a hospital-grade pump.