I’m not sure why Peter G’s response was voted as correct or voted up, it’s simply wrong.

Multiplying a Quaternion by a vector returns another vector, and the vector you multiply by should be a direction vector (representing a direction from the origin), not a set of floats representing euler angles in degrees. The result of that multiply operation is that direction vector rotated by the Quaternion.

In order to add two quaternion rotations correctly you multiply them: