The information under Type for this attack is not a mistake. This is exactly what is listed for Curse in the game and governs how it interacts with other moves that take type into account (such as Conversion and Conversion2).
Curse can function as two completely different attacks. Which one it acts as is based upon the Type(s) of the pokemon using Curse, specifically whether or not the pokemon is a Ghost-type pokemon.
If the pokemon that uses Curse is a Ghost-type pokemon (either normally or if the type is induced by the moves Conversion2 or Transform), the using pokemon will lose one half of its total HP (by integer division) and inflict a condition on the opposing pokemon. As a result of that condition, the opposing pokemon will lose one quarter of its total HP (by integer division) at the end of every round until it is switched out normally. Nothing other than switching normally will remove the condition from the opposing pokemon.
If the pokemon that uses Curse is not a Ghost-type pokemon, then Curse acts as a stat-altering attack. It will increase both the user's Attack and Defense stats by 1 step on the stat growth scale and decrease the pokemon's Speed stat by 1 step. As with all other stat-altering attacks, Curse may only increase or decrease stats by a maximum of 6 steps before it reaches the limit and will fail when used thereafter. Reducing the number of steps of alteration of one of the stats will result in Curse only altering that particular stat if the other(s) have already reached the maximum number of steps of alteration.
Both forms of Curse are unaffected by Accuracy/Evade modifiers.
