It's using the Bukkit API, so it's a Bukkit Plugin. Spigot is a modification of the implementation know as CraftBukkit. Bukkit != CraftBukkit, therefore Bukkit != Spigot.
It's using the Bukkit API, so it's a Bukkit Plugin. Spigot is a modification of the implementation know as CraftBukkit. Bukkit != CraftBukkit, therefore Bukkit != Spigot.