Think it is coincidence , the server just propagates the vlans to the client so you do not have to create the vlans on the client , You do have to manually assign vlans to the individual ports on the client or even the server for that matter that is the only way they get assigned to the ports . If you had origianlly made the client the server or whatever you may have made those ports the same by accident , no other way for that to happen.

Your VTP server switch sends BPDU to your VTP client switch. The vlan's you create and port assignment you create on your server switch are propagated to your client switch. This is the correct action of the server client relationship, VTP is use mostly in large network to make vlan assignment easier and less chances for config errors. Each time you make a config change the revision number will increment by one, if a client switch receives a BPDU with a higer revision number than it's own, it will change it's config according to the info in the BPDU. You can place the client switch in transparent mode and it will forward BPDU but will not change config. You should look into vlan pruning or usingthe "vlan allowed" command.