We may just have to agree to disagree here, recognizing that we're both drawing what we believe to be the best conclusions we can from very limited data.  I don't see the witches as mindless zombies.  The BOs, yes, but not the witches.  I'm not suggesting the witches are scheming masterminds, but they appear (to me) to have some capacity for rational thought and communication that the BOs lack.  I expect we'll learn more as time passes.
As to the fog, here's what we've seen it do (or happen at the same time):
- Acute respiratory distress
- Can be prevented, or at least minimized, by wearing a mask.  We'll probably find that garage lady's gas mask/respirator is much more effective.
 
 
- Skin and eye irritation
- Can be prevented, or at least minimized, by covering the skin with normal clothing.
 
- Can be neutralized by washing with soap and water.
 
 
- With concentrated or prolonged exposure, turn a person into a Burned One
- This one's still somewhat speculative--the only time we've seen this happen, a BO turned a person into another BO.  We assume--I think rightly, but still assume--that enough exposure to the fog will do it even without a BO attacking.
 
- I think it's also reasonable, though less certain, to speculate that it turns women into witches.
 
 
- Interfere with, though not completely prevent, electronic communication
- Including landline communication--the Internet at the office wouldn't have been wireless, nor would the phones, and the TV would almost certainly have had cable.
 
 
- Disable vehicles
- Exposure alone will do this, whether or not the engine is running.
 
 
- "Density" of the fog seems to correlate to difficulty moving about--when it's thicker, MC feels a physical barrier or impediment to movement.
 
The main classes of hazards are NBC - nuclear, biological, and chemical.  Does any of those explain these effects?
- Nuclear
- EMP would disable electronics.  Obviously this degrades communication, but things like the cell phones, TVs, and computers would cease to function at all, and we know that didn't happen.
 
- Nuclear radiation could easily cause skin burns, but they wouldn't be treated by washing with soap and water.
 
- We don't have any evidence of its causing things like BOs and witches, but I'll grant this one because "nuclear mutation" is such a common sci-fi/horror trope.
 
- EMP would disable modern vehicles (because they're dependent on electronics), but not older ones.  But it wouldn't progressively disable the SUV while they're driving it.
 
 
- Biological
- It isn't hard to imagine (particularly in a sci-fi/horror setting) a pathogen causing the turning (that's pretty much the Infected from N&T).  Its doing it in a matter of minutes is a little harder to accept.
 
- I think it's a bit of a stretch, but it could maybe cause the respiratory, skin, and eye sx with lesser exposure, and be washed off.  Maybe.
 
- But the fog?  Communications?  Vehicles?  I don't think so.
 
 
- Chemical
- I think this is the best fit, but still not a good one.  Specifically, in the form of a corrosive mist.
 
- Resp/skin/eye sx, check.  Wash with water to neutralize, check.  Ordinary mask/clothing acting to protect you from it, if imperfectly, check.
 
- Disabling vehicles--it could corrode wires or connections, or internal engine components.  Doubtful it'd be enough to do it in a matter of minutes, but plausible enough.  But strong enough to do this, and not be immediately fatal on unprotected exposure, is a stretch.
 
- Could affect antennae for various wireless communications.
- Maybe we hand-wave the landline comms by saying there were still wireless links that were affected?
 
 
- But the turning?
 
- Why don't we see any exterior corrosion on buildings, vehicles, or anything else?
 
- How does it act as a physical barrier?
 
 
So I really don't see a natural explanation that covers the effects we're seeing, which leaves something supernatural.  Whether it's that ancient native burial ground that was teased way back at the beginning, aliens, or something else, I have no idea.