Dns forwarders not validating
DNS packages doesn't contain information about its source and destination they are doing automatically using the DNS query cascade.
What you can do to know if it's working the forwarders or not is to set up a client with the Windows Server DNS IP as only DNS.
By using DNS forwarders you can improve the efficiency of name resolution for the computers in your network that query for DNS names outside your network (such as names on the Internet).
Visit Stack Exchange doesn't show the actual forwarder being queried.
The best ways to get the correct names and IP addresses of your ISP would be either to search for the list on your favorite search engine or simply contact your ISP’s technical support line.