That wide, ribbed stem looks like fasciation, where the growing tip splits into a flat band instead of a round stem. It can come from genetics, or from stress such as topping, damage, or a hormone swing, and in flower it often makes big, odd-shaped colas. The plant is usually fine, but dense flat buds hold moisture, so keep good airflow and check them for mold late in flower. It usually isn't passed on reliably, so if you want to keep the trait, clone it.