It makes you attack faster. It's just like a hunter's quiver or haste rating, in that increasing attack speed means your speed increases where as the number of your weapon speed will decrease. (2.6 speed is slower than 2.2 speed).
If you increase your speed then you're going faster, so the wording is correct. What's not correct is what Blizzard refers to as "speed" on a weapon's stats; "period" or "swing duration" would more accurate, as it is the time between attacks. A weapons "speed" should intuitively mean the frequency of attacks - the number of attacks per second or some similar measurement - i.e. a weapon with greater speed should attack faster...