So does Cho'gath's Feast.
So does Ahri's Orb of Deception.
So does Ignite.
They're all spells.
There's a difference between spell damage and magic damage.
Spell damage is damage dealt through a spell effect, which is generally considered any ability that requires a key press (Q, W, E, R, D, F, 1-6). The exception is with basic attack modifiers, as those change how a basic attack works, and with spells that apply attack effects (Ezreal's Q, Gangplank's Q, etc.)
Magic damage is damage that is reduced by Magic Resistance. It can be applied through basic attacks or spells, depending on the champion and their items. But most important to note is that not all magic damage applies spell effects.