Yup, it's software RAID. Same as pretty much any other onboard RAID controller. Looks like hardware RAID at first glance, but don't let it fool you. A hardware RAID controller has its own built-in processor and memory. The hardware controlls all RAID functions, so it requires little resources from your system. Software RAID relies entirely on your system's CPU and RAM and runs within the OS. So the speed of the RAID depends on the speed of your system.
The problem with software RAID is that since it runs within the OS, there's a chance the RAID could fail if your OS crashes. Hardware RAID doesn't have this problem.