Thanks for reporting this concern around the unwanted task notifications. Unfortunately, the subscription (following) is only supported for specific content or the place. If you're following the place (in this case, the project), you will receive notifications for content created within that place and there's no way to filter by author.
If this is an important feature you'd like to see in the future, I would recommend submitting a feature request idea in the Ideas for Jive space. Let me know if you have any other questions in the meantime.