This is the part worth understanding, because "smell proof" gets used loosely. An airtight jar works by blocking air. Nothing moves, so nothing escapes. A bag cannot do that, so it uses adsorption instead: activated carbon is riddled with microscopic pores, and odor molecules stick to them as air passes through. The air still moves. The smell does not come with it.
The practical difference is that a carbon-lined bag keeps working while you open and close it over and over, which is exactly how a bag gets used. It also means the carbon does the work, so a bag with a thin or decorative lining will not perform, no matter what the label says. Every carbon-lined bag here uses the same activated bamboo carbon lining.