einsteins,
No the 958 units do not have Side Imaging sonar.
For the “side scan” part:
They could be meaning the Side Imaging sonar that we use like Chuck stated.
They could also me referring to the “sidescan” word that we use in our “Connected Transducer” menu (called “Transducer Select” in older software).
They could also be referring to the sideways pointing beam of the WideSide transducer.