it shouldn't be bad for him, budgies live in flocks in the wild so it might even help him feel like there's other budgies around! i also play the radio or an audiobook for my birds when i'm not home, they sing and whistle at it haha so i guess they like it
as long as you interact with him plenty he shouldn't feel lonely, ofc it's better to have more than one since they're flock animals, but budgies like people so it's not bad to keep one alone if you give him plenty of interesting toys and attention every day! : D