That's because matt suggested that the plants had to be covered to retain more humidity(and that's what he do with all his TC plants), when they're in tissue culture, they have really high humidity because of the liquids, gel...etc, when is ready to take out, and you want to have them in invivo(isn't that how is called), they need sometime to adapt, so the bags are to retain more humidity so the plant doesn't died instantly, this also keeps other germs, air out that might kill the plant while it opens its stomata(i think when they're in tissue, it closes because there's no air going in to the plant, so the guard cells closes, and doesn't allowed any particle)(not sure if this right or wrong), once a week passed, they're ready to be open a little to start acclimatizing the plant to lower humidity, then another week, then they're ready to be out and treated like any other plant, so in 2 weeks they will be treated like any other plant i have, and slowly i will introduce it to direct sunlight.
Matt said they don't need light at this stage, they could died from it, since they're not used to, he said is not necessary at the moment, but it will be in 2 more weeks!
Hope it makes sense