If you have multiple connected Amazon Marketplaces connected, and have not yet selected a default marketplace the Communications' Performance page will default to "All Marketplaces".
If is is defaulting to "All Marketplaces" the statistics that show up on the dashboard will be a total of all the marketplace that are connected.
However, if there is a specific Marketplace you would rather see account information for you can adjust your Default Marketplace from your Settings. To get to your Settings, click on the envelope from your left navigation, and under Communications click on Settings. On this page, your third option down will be "Default Marketplace". From the "Default Marketplace" field, toggle to the desired marketplace. Click "Save" to apply any changes made.