I've heard the terms recently as well and they were explained slightly differently: Quiet quitters are those that do the job to the written expectation IE get the job done and work 40 hours when contracted to work a 40hr/wk job. The connotation is by not working 50, 60+ hours on a 40hr salary job and going out of their way to work themselves to exhaustion for the company, they're bad people. IMO it's a corporate term to degrade folks that only work to the job descriptions. I've no problem with doing 40hrs work for 40hrs pay but if someone does more than that, they ought to be compensated accordingly. I've seen how salaried folk age where I work, I'll stay hourly there.
Quiet firing I think is the same as your explanation: company basically doing everything they can to induce the person to quit; cutting pay and increasing workload in worsening conditions.
IMO, the switch of so many positions to salaried has caused a lot of this. Employers feel salaried means you're a wage slave that they can demand whatever hours they want out of you. In a normal organization like that, I'd rather be hourly so I can work my 40 and be done, or be paid extra to work extra. That's the way it should be. Thankfully my current position is salaried, but the boss is one of those rare managers that just wants the work done, not hours on a clock punched. As long as my work is completed, my manager doesn't care if I'm working 20 hours or 50. It tends towards 30 more often than not and we're both fine with that. I've had offers to go to positions making 20 - 25% more money, but 20 - 25% more time was demanded as well. I'm fine where I'm at thanks