Don't they mean the only American cargo carrier? I thought the Soyuz was the only capsule ferrying Astronauts to and from the station, at least until the Commercial Crew program gets to that point.
Dragon can return about 2500kg in total (though it is quite volume limited), and has special facilities such as cargo racks that can support, for example, a powered freezer to hold scientific samples requiring such facilities.
None of the other operational vehicles -- Progress, Cygnus or HTV -- have any cargo return capability.
So the quote is correct in two respects: firstly, Soyuz isn't generally considered a "cargo vehicle"; and if you expand that definition, Soyuz can only carry an extremely small amount of a limited subset of possible return cargo that does not include the most interesting payloads such as frozen biological samples.
When the Commercial Crew vehicles become operational in the next couple of years they will also provide some cargo return capability, but that isn't their primary purpose and will be fairly limited under most circumstances.
The second round of the Commercial Cargo program -- CRS2 -- has selected Sierra Nevada Corporation's Dream Chaser in addition to Dragon and Cygnus. Dream Chaser is a spaceplane that will provide substantial cargo return capability by landing on a runway. This will subject the payload to lower g-forces than Dragon and allow for a very short interval between leaving the station and cargo offloading and processing on the ground. Such capabilites will be extremely useful for returning delicate and time-sensitive experiments.
So, until Dream Chaser becomes operational, almost all cargo return capability will be provided by Dragon; and right now, the cargo that is returned not on Dragon is on the order of a rounding error.
You can take stuff back from the station in the Soyuz when it lands with returning crew, but space and mass are very limited. For example, Soyuz can't bring back the -80°C freezer with blood, saliva and urine samples from the astronauts (those are used, among other things, to calibrate exercise and diet regimens that lead to the least calcium loss from their bones in microgravity).
The Russian cargo vehicle is named Progress, and it does not survive re-entry.
Soyuz has another advantages over Apollo - like another module, separate from return capsule; together, those two modules provide livable volume 1.5 of Apollo's.
But for what we're talking Soyuz is more restrictive than Apollo.