Different birds have different personalities just like us.
They simply sound to be placid natured birds.
Just because they’re not directly interacting, it doesn’t mean that they dislike each other; they can still enjoy the company and security of having a budgie housemate.
The fact that they are not squabbling or harassing each other, makes me feel that they ARE suited to each other. If you’re a quiet person, you are unlikely to want a whirlwind extroverted person sharing your space!