Open Cascade is not an (open source) alternative to AutoCAD. Also there is none. (people talk about OpenSCAD and FreeCAD but neither of them are comparable to AutoCAD).
To clarify: Autocad is a CAD suite used for 2D and 3D drawing production. In addition to that, it is used as an implementation platform for a large number of third party domain specific software for engineering disciplines that need more intelligence on top of the basic Autocad - HVAC planning, civil construction and so on.
OpenCascade is a geometry modeling kernel - a c++ library with no "end user" gui functionality or database. Yes, such a thing is a critical part in a software like Autocad, but only one small part.
It's potentially important as there aren't that many projects from the 80s in the list, so maybe has an impact on the trend line.
(a trend line that would look similar if you look at time between proprietary alternatives I guess... a fact of the increasing amount of time spent on software engineering?)