In the example at about 5:01 only 100 units of negative charge are transferred from Object B to Object A with the result being that there is still a difference of charge between both objects. Object A is still " positive" with respect to Object B. Why wouldn't B give up another 50 units of negative charge thus making them both equally positively charge ?
It is well beyond the point of this video but... charge will transfer between two objects until the two objects have the same electric potential, not the same electric charge. Once more, that's not the point of this video. The point of this section of the video is that total charge is conserved.
