Except that that's pretty clearly not the case, as I explained in the post that resurrected this thread. The mechanic of hit points pretty clearly tells you which of those things happened, if you care to calculate it. The gameworld has logic. If I have a +2 to AC through Dex, and an attack misses my AC by 1, that's an attack that would have hit someone wearing identical armor, but with inferior dexterity. Therefore, it's quite reasonable to interpret that as a near miss due to dodging the attack. The mechanics give a window to the functioning of the gameworld.
Oh, and this whole section here is based on false assumptions.
You don't know that the "last 2 points of AC" are due to their Dex, and that is what causes it to miss. That's an assumption that you are making, not one that the game makes. AC bonuses aren't added in a specific order, there no range of AC that is assigned to a particular piece of equipment or ability (except possibly things like the Shield spell, which are added at the last possible moment to stop a hit).
You have a base AC calculation, which can be 10+Dex, or Armor+Dex, or 13+ dex due to mage armor or natural armor, but even that doesn't mean the AC from the armor is "first". It's just listed that way for ease of calculation.
Your Dex bonus could be what pushes you from AC 10 to AC 12, and 13 To 14 is due to a shield, and 15 to 18 is due to scale mail, meaning anything that misses by 4 or less is due to your armor. Or any other order you want to use. And what if you have a Ring or Cloak of Protection, or any number of other things that can add to your AC in addition to (or in place of) your equipment?
AC is abstracted to a single number that represents multiple ways of avoiding damage - some passive (armor, ring of protection), some active(Dex for dodging, the shield block - if you've ever seen a real sword and board fighter the shield doesn't just hang there, it's actively used to block), and so on.
It's all very much up to the DM and the player to describe how it functions, because the game mechanics only give you a single AC number to represent all those things. And Hit Points are part of it as well - they are equally vague and abstract and leave it up to the DM to describe a hit as "blow landing on your armor, but you feel the bruise forming underneath" or whatever you feel is appropriate. Or it may have been a psychic attack and the DM describes the headache and a trickle of blood from your nose as you drop below half hit points. Or hemorrhaging across your face as the mind flayers blast drops you to single digits and blood vessels burst in your skull. Or none of the above.
There are so many damage types in D&D that trying to create a single way of narrating hits, misses, and damage would be way too complicated and cumbersome. Which is why it's left up to the DM and players to narrate as much or as little as they see fit during combat.