I know that things you can get in buy mode aren't script mods but are traits and houses script mods??

Script Mods are when talented people write their own coding to change game behaviours, as apposed to pre-existing Maxis coding. A Tuning Mod is just altering the values of pre-existing Maxis coding. Houses are not Script mods, as that is the game saving houses in the Maxis coding, even if the houses contain CC. Trait Mods can vary, either changing a few values of Maxis code to have different effects, or writing your own new effects and subsequent new buffs that did not exist in game beforehand. Additionally, it also depends on what animations you want to attach to new traits. Pre-existing animations, or creating new ones. (One of the biggest, time-consuming challenges to undertake. Not for the faint-hearted.)