I wonder if it might be guessing based on the vector of the ways that connect at the node?  I've tried adjusting the ways/node so 635 is more direct, and 69 is more of an angle.  Reading the info at https://wiki.openstreetmap.org/wiki/Tag:highway%3Dmotorway_junction doesn't seem to have any way to clarify which way is the through-way, and which is the exit.