It is a SDR-based HF transceiver instead of wide-band SDR. SDR is implementation detail and extra feature. Most SDRs are receive only, and the ones that can transmit, like ones you listed, are limited in power.

The other difference is interface. The QSX, and other SDR-based transceivers, work like other regular transceivers. They have USB port for computer control and sound card output. Some newer radios provide I-Q input and output which can be used for more advanced modes. But the bandwidth is limited compared to the SDRs which can monitor an entire band.