I haven't researched it and I haven't even grown weed yet but I always erred on the side of overwatering seedlings. I figured that the roots gotta go nuts first in order to support leaves which fan out to grab as much sunlight and water as the plant will need. Looking at that dry ass soil made me want to reach for my watering can so if I were to make an uneducated guess, I would pick light proximity out of the 2 potential causes. It will be good to hear from the people who actually know what they are talking about though.
You will shake your head but I STILL find myself taking a deep breath when you are powering through the thick part of that bong hit. Not sure if it is moral support or wanting a good bowl for myself on the weekend days.
Definitely not underwatered.. that causes droopy leaves