Does a land that becomes a creature count as a creature spell when cast?

When you play a land, you are not casting a spell. CR 305.1 states that playing a land is a special action — it does not use the stack and cannot be responded to. Because it never enters the stack as a spell, it is never a 'creature spell,' regardless of any creature-granting abilities it may have.

A card's status as a 'creature spell' only applies while it is on the stack after being cast (CR 111.1). Lands are explicitly excluded from being cast under normal game rules (CR 305.1, CR 601.1). Even if a land card has the creature type or gains creature characteristics (e.g., via its own ability once on the battlefield), this does not change how it enters play.

This distinction matters for effects like a Thalia, Guardian of Thraben (which taxes noncreature spells) or Spell Snare (which counters spells). Neither can interact with a land being played, because the land is never on the stack as a spell at all.

Example: You play Mutavault from your hand. Even though Mutavault can become a creature, it enters the battlefield as a land via a special action. Your opponent cannot cast Counterspell to stop it, and Goblin Charbelcher's 'find the first non-land' calculation would still treat it as a land in the library.