NXDOMAIN but still get it...

[Bernard Fay]

[ ~]# *nslookup centos.mirror.iweb.ca <http://centos.mirror.iweb.ca>*
Server:        172.21.241.18
Address:    172.21.241.18#53

** server can't find centos.mirror.iweb.ca: NXDOMAIN



But ...



[ ~]$ *nslookup iweb.ca <http://iweb.ca>*
Server:        172.21.241.18
Address:    172.21.241.18#53

Non-authoritative answer:
Name:    iweb.ca
Address: 174.142.1.18

[ ~]$ *nslookup mirror.iweb.ca <http://mirror.iweb.ca>*
Server:        172.21.241.18
Address:    172.21.241.18#53

Non-authoritative answer:
Name:    mirror.iweb.ca
Address: 192.175.120.177

[ ~]$ *nslookup centos.mirror.iweb.ca <http://centos.mirror.iweb.ca>*
Server:        172.21.241.18
Address:    172.21.241.18#53

Non-authoritative answer:
Name:    centos.mirror.iweb.ca
Address: 192.175.120.169



What am I missing?  There is definitely something I do not understand.
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