What this video covers
The clip is about why moldy drywall is replaced rather than cleaned.
Drywall is porous and faced with paper, which is exactly the food source growth wants. Roots penetrate that paper layer, so surface cleaning removes the appearance while leaving the colony inside the board.
The takeaway
Affected drywall gets cut out and replaced. Cutting back beyond the visible edge is standard, because the growth extends further than the staining shows.
Read the full written guide: Mold in Drywall.