NASA News item Ground Segment Testing a Success for NASA’s James Webb Space Telescope says:
Testing teams have successfully completed a critical milestone focused on demonstrating that NASA’s James Webb Space Telescope will respond to commands once in space.
Known as a “Ground Segment Test,” this is the first time commands to power on and test Webb’s scientific instruments have been sent to the fully-assembled observatory from its Mission Operations Center at the Space Telescope Science Institute (STScI) in Baltimore, Maryland.
Since reliably communicating with Webb when in space is a mission-critical priority for NASA, tests like these are part of a comprehensive regimen designed to validate and ensure all components of the observatory will function in space with the complex communications networks involved in both sending commands, and downlinking scientific data. This test successfully demonstrated the complete end-to-end flow from planning the science Webb will perform to posting the scientific data to the community archive.
I don't know where JWST is at the moment, but I'm pretty sure it's on Earth and not very close to any of the Deep Space Network dishes. Unlike lower frequencies, the bands used for deep space communications won't reflect off of the ionosphere, so rather than linking to the DSN and letting that system broadcast to JWST, the Mission Operations Center at the Space Telescope Science Institute (STScI) in Baltimore, Maryland must have used the internet and either a mock-up of the DSN converting to S or X-band locally, or they bypassed the radio link entirely.
Is it known how this was done?