From my perspective: that's the point of the web toy. It shows who was using these em dashes before they were likely copied and pasted from ChatGPT (or generated from APIs). The em dash is widely identified as a single character that highly increases the "smell" of text as being generated by AI.

It is novel to see which users were producing text with an em dash before the rise of AI slop. User 'derefr' was 5 years ahead of everyone.

I do wonder if there was some journalism CMS involved, or if these users figured out how to produce the character on their own volition.

EDIT: 'lynndotpy' has an explanation in this thread.