lmao. that's just a nice sturdy joint where the branches form. it's not preflowers, it's not a disease. it's a good thing. it's what you want. it means the plant is doing well and preparing to hold up the weight of the buds.it's somewhat rare in my experience to see it on such a young plant, but then again i veg with floro lights.
edit: i just snapped a pic of one of my own plants to show you. ignore the dead leaf, though. this plant was a guinea pig for some fertilization experiments i've been running and it hit a bump a couple weeks back. this is the only one that's far enough along to have the knobs. i assure you it's 100% normal.