Hmm. So there's a wording distinction here.
The druid stuff says "... drop to 0 hit points", and later says "if you revert as a result of dropping to 0 hit points", and then says "as long as the excess damage doesn't reduce your normal form to 0 hit points, you aren't knocked unconscious."
Disintegrate says "If this damage reduces the target to 0 hit points, it is disintegrated."
Note that "drop to 0" and "reduces to 0" are not precisely identical.
The combat rules say: "If damage reduces you to 0 hit points and fails to kill you, you fall unconscious."
On careful reading, I conclude that these rules are not rigidly structured enough for us to draw definite conclusions from the distinction. It seems to me that clearly spell damage that "reduces you to 0 hit points" has caused you to, at least temporarily, "drop to 0 hit points". Wild shape (and other polymorph effects) would presumably proc on that. But that doesn't mean you were never reduced to 0 hit points; it just means that a specific thing happens. Other things that happen on reduce-to-zero might also happen.
So here's a question. Imagine that you have a suit of armor which says that, if you are reduced to 0 hp, it casts a cure light wounds on you, restoring d8+3 hit points. You have 8 hit points total. You take 17 hit points of damage from an attack. What happens?
1. You die. Because the damage in excess of your hit points was more than your hit point maximum, therefore dead.
2. You are reduced to 0 hit points, the armor procs, you now have d8+3 hit points.
3. You are reduced to 0 hit points, the armor procs, you now have d8+3 hit points and take the remaining 9 of damage, which may knock you unconscious but cannot kill you outright.
Now, what happens if the armor proc is explicitly stated to work when wildshaped, and you are wildshaped when hit?
Does the armor proc *replace* the revert? Does it not happen because the wildshape revert happens first? Do they both happen?
The druid stuff says "... drop to 0 hit points", and later says "if you revert as a result of dropping to 0 hit points", and then says "as long as the excess damage doesn't reduce your normal form to 0 hit points, you aren't knocked unconscious."
Disintegrate says "If this damage reduces the target to 0 hit points, it is disintegrated."
Note that "drop to 0" and "reduces to 0" are not precisely identical.
The combat rules say: "If damage reduces you to 0 hit points and fails to kill you, you fall unconscious."
On careful reading, I conclude that these rules are not rigidly structured enough for us to draw definite conclusions from the distinction. It seems to me that clearly spell damage that "reduces you to 0 hit points" has caused you to, at least temporarily, "drop to 0 hit points". Wild shape (and other polymorph effects) would presumably proc on that. But that doesn't mean you were never reduced to 0 hit points; it just means that a specific thing happens. Other things that happen on reduce-to-zero might also happen.
So here's a question. Imagine that you have a suit of armor which says that, if you are reduced to 0 hp, it casts a cure light wounds on you, restoring d8+3 hit points. You have 8 hit points total. You take 17 hit points of damage from an attack. What happens?
1. You die. Because the damage in excess of your hit points was more than your hit point maximum, therefore dead.
2. You are reduced to 0 hit points, the armor procs, you now have d8+3 hit points.
3. You are reduced to 0 hit points, the armor procs, you now have d8+3 hit points and take the remaining 9 of damage, which may knock you unconscious but cannot kill you outright.
Now, what happens if the armor proc is explicitly stated to work when wildshaped, and you are wildshaped when hit?
Does the armor proc *replace* the revert? Does it not happen because the wildshape revert happens first? Do they both happen?