Maybe he has a feedback loop, and depending on how it uses it, it could actually have something that is called "constant current stepper driver" or chopper. Just a mention, mosfets are used as switches either way. The only other method to use mosfet would be as an amplifier which is not the case. In the syntagm "constant current driver", the coil current although called constant, its actually a sawtooth wave, not really constant per se, although if somebody zooms out far enough it appears to be.
Current device or voltage device, this syntagm refers to the type of input of the device, or how it is controlled. About what the output function depends on. E.g. mosfet input is gate, and the function of the mosfet depeends on the gate voltage, therefore mosfets are dubbed voltage devices, all of them. The old type transistors input is base, and the function describing the collector and emitter depens on the current that is being fed into the base, hence all those transistors (bjt, igbt) are dubbed current devices. An microcontroller which has logic level on voltage like 1.8v, 3.3v or 5v it is also a voltage device.
Current device or voltage device, this syntagm refers to the type of input of the device, or how it is controlled. About what the output function depends on. E.g. mosfet input is gate, and the function of the mosfet depeends on the gate voltage, therefore mosfets are dubbed voltage devices, all of them. The old type transistors input is base, and the function describing the collector and emitter depens on the current that is being fed into the base, hence all those transistors (bjt, igbt) are dubbed current devices. An microcontroller which has logic level on voltage like 1.8v, 3.3v or 5v it is also a voltage device.