All new birds are quiet, whether male or female, in the first few days you get them
Four days is still very early to tell if he's happy, or chirpy. I'm sure in a week or two he'll be more settled in and begin to move, play, and vocalize more.
Silence means danger to budgies, so you should play some quiet background music to make him feel safer, you can also cover his cage on three sides as it means security.
Tweety is beautiful!