ROS 3.x pretty much EoD, ‘End of Development’ and ‘End of Download’, so point to work on errors there.
Current documentation http://wiki.mikrotik.com/wiki/Category:Manual, unfortunately even this is not without errors.
In addition, the excerpt you posted is correct. First connections are marked based on source address. That connection mark is applied to traffic bidirectionally, so both upload and download packs have the connection mark. Based on the connection mark a packet mark is applied to all upload and download packets. Now all packets in that direction have a have packet mark. Then upload and download queues are created, and attached to interfaces, with a reference to the packet mark. Interface queues only see packets that are sent out to the wire through them. Therefore the upload queue sees all packets with that packet mark going out the Public interface (upload), and the download queue sees all packets with that packet mark going out the Local interface (download).