The direction of the currents simply follows from the polarity of the voltage in each case, but this section of the transcripts shows the presenter of the video is talking about the change of magnitude of the collector current in response to a changing base current:

6:02 an NPN bipolar is like a switch which is normally open. it won't conduct until a current is applied at its base terminal. PNP types on the other hand act in the opposite way they reduce the flow in relation to their base current.