In the case of the Chinese wheelbarrow, that is correct, but the sail is an improvement added later to the existing conventional design of the region and era which happened to use a central wheel.
I'm no expert on international wheelbarrow histories, but assume that the term "sailbarrow" being so general applies to any wheelbarrow having a sail. The historic precedent of the Chinese incarnation is literally their conventional wheelbarrow with a sail added.
I assume the same approach can be (and probably has been) used on any wheelbarrow in appropriate conditions.
The sailbarrow has a large central wheel that bears the weight, relieving the human of the need to personally support the weight of whatever's being carried.