memes

Using honest to goodness em dashes instead of just a hyphen - pretty uncommon.

Even a hyphen would be pretty unusual in a real text message, because they're more annoying to get than other common punctuation on the phone keyboard, and autocomplete won't put them in.
In a chat app, a hyphen would probably be somewhat common since it's right there on the keyboard, but a true em dash would be pretty unusual since most chat apps aren't going to be doing autocorrect like a word processor would, and you'd have to use the magic key combination to insert it.

But we don't have the original text so we can't tell if the original author confused a hyphen with an em dash, though

It's basically unseen outside of professionally written stuff. Most people use commas. But AI like to use them a fair bit, more than the average internet user.