I suppose it depends what is popularly meant by 'Metroidvania.' To me it means an action platformer with the ability to upgrade your character and explore for said upgrades in a relatively non-linear fashion. The original Metroid released in 1986 certainly had that. The original Castlevania was more staged based but Simon's Quest released in 1987 had both of those elements. Never mind the fact I'm sure there were other games of the genre that delivered the same elements and possibly predated those but didn't have the good fortunate of being as popular.

In any event -- Terraria is probably more like original Metroid and Simon's Quest than it is a 'Metroidvania' if people want to exclude those from the descriptive.

I'm fairly certain Delve Deeper installed XNA on my computer too. And not quite sure, but I think Magicka did something with it too, not quite sure though, but the game refusing to run on my computer because of an exception somewhere in the Microsoft.XNA assembly (unable to find graphics card which fills the requirements) might be a pointer.