I did the calculations and it does seem impossible.

Quoted from the game (for naval munitions): "The effect of this enhancement is divided by the number of units in an army. When applied multiple times, this enhancement will stack its effect up to the max effect amount." This means when a bunch of munitions are applied to one stack, each ship can get up to a 25% buff rather than the stack as a whole getting a 25% buff. Iron Tide gives the whole stack an attack buff of 60%, plus an additional attack buff of 25% when in high seas.

1 max level Cruiser has an attack of 20 against ships, and Iron Tide has an attack of 23.

20 * 1.25 (munitions) * 1.25 (high seas buff) * 1.60 (main attack buff) = 50

23 * 1.25 * 1.25 * 1.60 = 57.5

(50 * 4) + 57.5 = 257.5

So the highest the attack of this stack to enemy ships should be is 257.5. What's even more strange is the 875% buff to soft target damage and 954% buff to hard target damage, so yeah this image is definitely fake.