I'll buy that the lower temp could be for them. Lower temps do allow more oxygen and also does slow metabolism possibly extending the life of the fish. But, lower temps do lend themselves to much higher rates of infections and parasites.
As for the rest of it, tank size maybe. As for the plant, NO WAY! I don't know if they simply don't know or don't care but the plant is a houseplant that requires dryer well drained soil and the stalks of the plant rot if it is too wet. Might as well keep the betta in a bog. I saw another example, and almost an identical article written about keeping bettas with Lucky Bamboo.
This seems to be a classic example, if they actually get this to work, of someone who has found a perfect situation that has to be maintained perfectly for it to have a chance to work. Definately not a good idea for anyone else to try unless they know exactly how it is being done and follow it to the letter.
I will stick with keeping them in 2.5-5 gallon tanks with lots of good aquatic plants.