Thanks, I understand now. The widget actually shows a mashup rather than a map. A mashup is a map that shows all the locations from the maps in one or more posts.
There’s a radio button on the widget to select a default query or you can enter a custom query. You are probably seeing the POIs from the current posts (which is the default selection).
To show just the map(s) from a specific post, enter the post ID or page ID in the query field like this (where 1234 is the post you want to show):
There’s more information on queries and mashups in the documentation: