Yikes, yeah your latest post was definitely not about classical music. That comes from your channel settings. The code will pick 1 community for you based on previous posts, unless you select a community on the "Publish" page. You will see a "Community override" box right there on that page that let's you select a community yourself.

Also, in your main channel settings screen, be sure the communities that are selected there match the kind of posts that you put up. Ping me on matrix or twitter and I can do a screenshare with you too..