A kind user shared with us this information.
Take a look at this if you want to prevent posts that are fetched via WPeMatico to be published on social media with the build-in sharing via Jetpack.
When WPeMatico fetches a post it triggers to share the post on all public social media links. This is through Jetpack plugin.
If in Jetpack (https://wordpress.com/marketing/connections) the setting “Connection available to all administrators, editors, and authors” is enabled for any connection, all posts created by WPeMatico will be auto-shared.
If the connection is private and publishes the posts as another user via WPeMatico, this does not happen.
Then, apart from the private connection, use a different user in your WPeMatico campaign.