I think, for the sake of this article, you could consider Slack a household name. It doesn't mean everyone has heard of it, it just means "well-known". It's a publicly traded company, and I'd say the average person (especially in America) likely knows what it is.

I guess I don't really watch many movies that delve into 21st-century office communication, but I imagine if I did their chat app would be modeled after Slack.

Overall, though, this is a minor point compared to the rest of the article.