I was curious about this as well and have done a bit of research. Basically, “A “block” can be a paragraph, a blockquote, a list item, etc. In general, anything that has empty lines before and after is a block.”
This means, you were creating a “block” that was only a heading. In fact, it seems to me you don’t need Obsidian’s block references at all, you just need to use the “heading” reference, as described by Ryan here, because this type of reference grabs the heading and all of the content under it until the next heading
If you’d like to try and create multi-paragraph blocks without headings, here’s another approach.