Going by the definition given here, it appears to be an ottoman.
"Traditionally, a hassock's covering is so extensive that no legs or framing are visible, unlike an ottoman. Another difference between the hassock and the ottoman is that an ottoman usually has a central space available for storage, while the hassock does not. Lacking the storage feature, hassocks tend to be smaller than ottomans."
Here's the object in question for those not familiar:
Legs are visible - Ottoman +1
Appears to have storage (if you look closely, there's a large line between the top of the object, and the next section that the legs connect to - this cover appears to be removable) - Ottoman +1
Ottoman 2, Hassock 0