How did they do this? AC is so hideously expensive, even using the chain shirt stacking trick, it's still inefficiently expensive.
Start with a party with members who can (and will) craft magic items.
At 14th level, you've got 150,000 gp.
So...
10 base
+6 shield... +4 heavy shield (8,000 gp)
+12 armour... +4 mithral full plate armour (8,000 gp +9,000 gp for mithral)
+4 deflection... +4 ring of protection (16,000 gp)
+4 natural... +4 amulet of natural armour (16,000 gp)
+2... Greater Heavy Armor Specialisation (Races of Stone, pg 141)
+1... Shield Specialisation (PHB2, pg 82)
+1 dodge.... Haste spell/boots of speed
+1 insight.... Dusty Rose Ioun Stone (2,500 gp)
+3 Dex... Dexterity 16 (aided by +4 belt of Dexterity, 8,000 gp)
total: AC=44; total cost 67,500 gp.
Typical CR 14 attack bonuses:
Nalfshnee: Bite +20 melee, 2 claws +17 melee
Nightwing: Bite +18 melee
Truly Horrid Umber Hulk: 2 claws +26 melee, 1 bite +24 melee
Werewolf Lord: Bite +25 melee or Claws +24 melee or Sword +27 melee
The thing is... I'm not actually trying very hard. They had even more bonuses than those above. One of the PCs had a dip into Psionics and ended up with his shield and normal armour also adding to touch AC.
It should be noted that this isn't part of the "Wizards vs Fighters" debate; this build presumes clerics or wizards in the party helping the fighters even more (and incidentally breaking the maths of the game).
Cheers!