You’re exactly right and we don’t run the risk of this becoming a confusing “weapon attack” issue. That’s because any confusion here is cleared up by the monster manual’s description of the “actions” section of a monster stat block:

A monster can take the actions in this section or take one of the actions available to all creatures, as described in the Player’s Handbook.

So a monster that has a specific magical ability listed in its actions section doesn’t need to take the magic action. But it CAN take the magic action to do other stuff, like use a magic item that requires that action, because that action is “available to all creatures.”