金剛經纂要刊定記 4.309

4.309

名逆流者。逆凡流也。謂若取六塵即入凡流逆聖流，既不取著即入聖流逆凡流也。

"Called going against the stream" means going against the stream of ordinary beings. That is to say, if one grasps the six sense objects, one enters the stream of ordinary beings and goes against the stream of nobles; since one does not grasp or cling, one enters the stream of nobles and goes against the stream of ordinary beings.