I have only pointed the A records and Name server of the domain in the domain-registrar control panel. I have not created any domain or DNS for this domain in ISPCONFIG, yet when opening this domain page in the browser the default page from ISPCONFIG server is served in the browser. I am sure this is not the correct behavior or is it?
Thats the correct behaviour. If you create a dns record, then the domain gets pointed to your server when you enter the domain name in the web browser.
You are right, but I have not created any DNS record for this domain on ISPCONFIG Server. I have changed the DNS record in the domain registrar records.
You created the dns record on the authoritive DNS server, this does not has to be the ispconfig server.