Leafs are fragile. Excess air movement and friction, or any abrasion of the plant to even itself, can result in that. Nothing to sweat, youâre all good. Healthy looking seedling. Youâll be fine, keep up whatever youâre doing.
Cheers
Sometimes insects can invade your space and feed on leaves. I've seen tiny grasshoppers leaves marks like that until I find 'em and pinch 'em. Other than that heat stress can make leaves brittle and they can crack.