Dual radio refers to the option to have either a 2.4GHz and a 5GHz radio, or two 5GHz radios. The Software selectable radio refers to the Software Defined Radio (SDR) process that you can enable that will scan the surrounding environment and choose a channel based on those scans. It can also go to a different radio if it finds no suitable channels on the first radio. For example, if it finds no usable channels on the 2.4GHz radio, then it will switch to the 5GHz radio instead.
Here is a guide that reviews SDRs in case you're interested- https://thehivecommunity.aerohive.com/s/article/SDR-Profiles
