There is a difference between an “active column” and an “active cell”. Spatial Pooling provides a stream of active columns representing spatial information. The TM algorithm operates within that space. It only activates cells that are within active columns. You’ll never see a cell activate in HTM outside of an active column. This means that the proximal input is the ultimate driver of cell activations.
I don’t know the exact neuroscience of how proximal input is shared by the cells within a column.
I explain the two conditions that cells become active at 5:32 in the video.