The notification service you're using to stay informed about who is adding you to the lists does not check if you are already on the list either. It sees that you've been added to the list and sends you another message, regardless of if you were already on that list or not.
Either could keep track of who they have already added to a list to avoid adding people to the same list multiple times or sending out duplicate notifications but neither does.
I believe that the one sending notifications has more responsibility here because there would be no sign when using the regular Bluesky you've been added to a list twice without that service sending the messages to you.
You can't even directly see that you've been added to a list in the regular Bluesky interface/app.
2. I do not believe that the two services are run by the same people. There would be little point for the same person to make a second one covering the same topics. I do suspect they may use the same automation software and maybe even similar criteria (e.g. hashtags used) to make their lists though.