Same for me. It was immediately obvious I should scroll, but I don't know why.

I was viewing on desktop and the blank space all around made it immediately feel like an article that required a scroll to view the content below the fold.

Seeing the timestamps change as I scrolled and seeing a progress "bar" update within the speech balloons during the dialogs made it more obvious I just had to scroll to see the content change.

I do think the progress bar color is low contrast enough that some might not see it and not realize they have to scroll to cause the dialog to update, though.