Do notifications know about each other?

I have a service that tends to act up on the weekend and that is fine. But he should only complain once and tell me when hes okay again.
I manage most notifications based on hostgroups, which works great. Now that services host is part of a group but i just want that specific service to complain just once, not the entire group.
So i created a new notification that is only triggered if it has that services host name and service name.
This weekend it spammed messages again so i think its still triggered by the group notification and maybe even separately by new one aswell.

Is it right that i should add a rule to the group notification that says is not XXX or did i mess up something else and they should exclude one another?

Notification rules have no clue about the existence of other rules. If you want something to be excluded from one rule, it needs to be excluded, otherwise both rules may trigger a notification.

This is by design I suspect, as we have many use cases that rely on this logic (ie, send a slack notification for X users, and an email for Y users).

If you only want 1 rule to apply to this service, you need to make sure that the rules are setup in such a way that only the desired rule matches.