A bus switch type uses pullup resistors for level-shifting. Since this is a simple MOSFET switch, it does not have any inherent drive capability (Figure 1).
A bus buffer type uses the output of a CMOS structure for level-shifting. Therefore, it has an inherent drive capability and provides a digital output (Figure 2). For the drive capability, see the output current value shown in the Electrical Characteristics table in a datasheet.
The following shows the equivalent circuits of a bus switch and a bus buffer.