Strange houseplant behaviour?

I have a cluster of 3 "dragon trees" in a pot. They have long green leaves with red striped on the edges of the leaves.



I recently watered it heavily and gave it a lot of sun. A few days later, all the leaves on the bottom 5 inches of the plants died and came off, but the rest of the plant looks fine. The plants are about 4 feet tall.



Did I cause this by watering it? What happened?

Strange houseplant behaviour?
it may be normal as the plants transfers energy to new growth