This is functioning as designed- When you create a watch it is always created on all models of the same model type not just the single model you have used when creating the watch.
When you create a watch on a model it is also created on models of the same model type along with modeltypes that are derived from that modeltype if you choose the “Make Inheritable” option.
So for example If you create the watch on a SwCiscoIOS model, all SwCiscoIOS models will have the watch but no other models of other types will.
If you create a watch on a GnSNMPDev model and you have the “Make Inheritable” option selected, nearly every device in your database will have the watch.
There is no other way to group watch creation because watches are actually created as attributes on modeltypes, so they are modeltype specific.
If you only want to have a watch on a single or selected model you can make the watches inactive by default and then activating them on the actual models that you need it on.