The bigger problem here is that Slack AI has a misfeature where malicious instructions can cause it to answer questions with links that leak data. The specific examples aren't as important as the overall class of attack.

Anything you say in Slack - or anything in a document that is available within Slack - could potentially be leaked to an attacker who manages to get their malicious instructions into your Slack. There are many ways they might be able to do that, such as tricking an employee of yours into uploading a file to Slack that includes those instructions.