query restricted on sub domain

[ChrisC]

I have set up Bind 8.2.4 on solaris 9, as a secondary server. I
restrict resolving queries on the server with the line at the top

allow-query { "access-list"; };

Then for each of the authoritative domains I have 

allow-query { "any"; };

which works ok. 

For one of the domains we have a sub domain for it -- which is served
off 2 other servers e.g. usa.domain.com and ie they have different ns
records but for some reason I am seeing queries for it in the messages
file on the main server which serves domain.com.

denied query from [151.164.1.15].15876 for "www.usa.domain.com" 

My question is

- why am I getting queries for usa.domain.com when it is served off 2
different servers elsewhere ?

The server does however give the locations of the ns and soa servers
for the sub domains. This makes sense as if they did not then nobody
would get answers from there.

Thanks