There's probably pretty good reason this specific bit went open source. The vision tracking community usually tends to make leaps and bounds on open source projects. People will easily be downloading openCV and modifying it in different ways for their home projects. These modifications will then be usefull to darpa.
Considering that the vision tracking isn't a core function of one of their devices they probably aren't as interested in hoarding it. Why not let some other people do the work?
What are the engineering and design challenges in creating successful IoT devices? These devices are usually small, resource-constrained electronics designed to sense, collect, send, and/or interpret data. Some of the devices need to be smart enough to act upon data in real time, 24/7. Specifically the guests will discuss sensors, security, and lessons from IoT deployments.