If it cites em dashes as proof, it came from a tool

OP should learn a thing or two about probability distributions.

Yes, anyone could write an em dash if they wanted to. Few people did, because to most it was additional effort without making a difference.

If in a random text in a situation where em dashes were hardly used before, they are suddenly used everywhere, something is fishy.

Medium forces an em dash when you input `- ` between characters