2 Answers
They are two completely different services.
Amazon CloudWatch is a monitoring service for AWS cloud resources and the applications you run on AWS.
AWS Config provides you with an AWS resource inventory, configuration history, and configuration change notifications to enable security and governance.
Check out the FAQs here:
CloudWatch – Monitor resources/logs for trends and exceptions
Config – Monitors resource configuration for drifts; can setup trigger to enforce drifts like when using the wrong instance type
This looks interesting: https://stackshare.io/stackups/amazon-cloudwatch-vs-aws-cloudtrail-vs-aws-config
Awesome reference