Maybe they just picked the best fit. IndigoVision cameras have to be capable of delivering multiple 30fps streams because their basic system cannot redistribute a single stream. They require either a proxy server or a "gateway" to take one stream and distribute it as two or more. IV recommends using a TCP/IP stream for recording and a multicast stream for live viewing. A number of cameras, including all of the Axis cameras we tested, were unable to deliver two 30fps streams simultaneously.
IndigoVision also uses most cameras' ONVIF profile or they require a "camera gateway". Camera gateways and proxy servers add cost to a system and have bandwidth limits.
Granted, the 5k camera can't deliver 30fps, but as the article states, "the IndigoVision Ultra 5K delivers ten times better low lux performance and double the frames per second than other ultra-high resolution cameras."