Let's run some numbers.
A usual BIS 2hWP build (5 Warlord - 4 Vic) + 2 pc Genesis reaches 876 STR (1026 buffed) and also has 99 (Warlord 5pc) + 60 (Bloodlord) + 18 (Vic gloves) + 36 (genesis piece) = 213 melee Power. All in all, their DB will be (1026+213)/5 = 247.8
The AA damage formula before modifications is (wDps + 0.50*DB)*wSpeed
That number is then multiplied by both the Dmg% bonus (25% from Divine Fury tactic and 5% from Bloodlord weapon) and by the AA dmg% bonus (25% from Fanaticism tactic and potentially another 25% from an IB's Blood of Grimnir).
- No IB buff:
(82.6 + 0.50*247.8)*4.2 * 1.30 * 1.25 = 867 * 1.30 * 1.25 = 1409
- With IB buff:
(82.6 + 0.50*247.8)*4.2 * 1.30 * 1.50 = 867 * 1.30 * 1.50 = 1691
Even if we consider unconventional build adjustments from the WP's side, we still can't reach 1778:
Usually 2hWPs have crit talismans in the 3rd Jewelry slot and use linis offering crit (usually TOU+crit).
Swapping out the crit talisman to a +54 Melee Power tali and the liniment to Inevitable Tempest (STR +Melee Power) while also under an IB buff, we get:
(82.6 + 0.50*266.2)*4.2 * 1.30 * 1.50 = 906 * 1.30 * 1.50 = 1766
Close but no ciggar
As we can see, we are still off from the observed 1778 AA hit even with an IB buffed regular or unconventional BIS 2hWP.
But in this case, the 2h WP in question is not even in BIS gear (Warlord-Bloodlord mix). So something else is at play here.
The difference can be explained in the following ways:
- An incoming dmg tanken increase% on the target:
E.g. from an Engi's Signal Flare or from a BW's 7pc Warlord proc

- A warcamp buff/debuff:
Another commenter seems to imply that was the case and it could certainly explain the dmg increase.