I just read the announcement. He's working solo on Haunted Chocolatier and says this about Stardew

with 1.7 I have been trying to take more of a “creative director” role in the team, so that (at least for now) I can focus the vast majority of my attention on Haunted Chocolatier.

and also

in order for me to maintain a full connection to the game, I need my hand to touch every piece of new content. And there are some aspects of content development which I insist on doing myself, like the music.