I think that is only the case if there is a line break between text and the dashes, see Basic Syntax | Markdown Guide
You can probably notice it preview mode a little better (Ctrl + e).
The markdown files didn’t have anything especial, I pretty much was trying out what you showed in your video. The only difference for me was having an extra blank line between the three dashes. This one wasn’t added:
Test? #flashcard #tests
Here is the answer
---
This one was
Test? #flashcard #tests
Here is the answer
---
This is good to hear!