Same situation as you here.

From what I gather, even if you use USB teether or hotspot or 4G modem, it'll still activate the hotspot clause. Because some mobile dataplan have unlimited data. However, that's for the phone only.

If you use this dataplan to run your PC broadband, it'll activate the hotspot which has a limited quota of say 6GB monthly depending on the plan.

Not sure if my understanding is correct or not. But I think it is, else everyone will start using mobile data plan as their main broadband.