This seems a lot like you making assumptions about their expectations and/or acting on their expectations/your assumptions; rather than acting the way you think is correct.
If you aren't their personal dev, then don't be one. The only thing my presence in a client's slack means is that I (and/or the other people from my company in their slack) am reasonable first point of contact. I'm perfectly happy telling them that their problem is not one I can solve (or choose to prioritize), and that they should touch base with <appropriate person>.
I guess my story was unnecessary, but I commented that I didn't read the article the way the person I responded to (and the person above him as well). I don't understand why the top rated comment is worded in a way that sounds like the article was bashing slack because the Author of the article doesn't understand how to focus...when I read the article and saw nothing that led me to believe the top level comment was on topic. So I commented.
If I am ok to carry on this tangent we are already on, I cannot wrap my head around a scenario where it would be appropriate for a member of a SaaS company, dev/PM/CTO/QA or what have you to be in a slack channel for one of their clients. It's completely unprofessional and should be avoided.
If you aren't their personal dev, then don't be one. The only thing my presence in a client's slack means is that I (and/or the other people from my company in their slack) am reasonable first point of contact. I'm perfectly happy telling them that their problem is not one I can solve (or choose to prioritize), and that they should touch base with <appropriate person>.