No, scenarios are not "mods", it just got lumped into it. Civ scenarios, going back to at least Civ2, have always been a distinct thing from the developer (Microprose) as well as user-community ones. They are well thought out and in many cases, just as in-depth as the regular game (on the scale of DLCs), usually with a complete makeover. Mods came about when people started dinking around with the files (graphics and otherwise) to see what they could come up with. Scenarios, at least the good ones, can use mods/modpacks but Civ scenarios have always been real, standalone games. CivFanatics and Apolyton have always made that distinction.