I think this is a textbook example of trademark infringement all wrapped up in a nice neat little package. It shows how brand protection shouldn't really care about the intent of the infringing party. It's so overt I'd have to assume it was due to naivety, but that doesn't make it any less damaging.
The fact that it just doesn't "feel" like a service that might follow from the team who brought us Slack-the-team-chat-product just serves to establish Slack Technologies' ownership of their brand, and their need to protect it. If their marketing and PM teams have seen this, I'm sure they're cringing.
That's not to say that it doesn't offer value. I'm sure that if the branding issue wasn't so overt, we'd all be cheering it on as a Show HN style MVP.