Re: I'm assuming
You are forgetting that the router could redirect DNS to wherever 'it' wants IF the correct ACL/Firewall Rules are setup.
(Assuming a router that has at least some facilities to setup Firewall rules etc)
This can also be performed by your ISP, if they desire, so ALL DNS goes through the ISP's DNS Servers.
(Was not uncommon in the past !!!)
I have configured my Home Router to redirect all port 53 calls to 'My Filtering DNS Server', allows lots of crud to be filtered out before you transfer it across the internet to be filtered by browser addons etc.
(I know it does not protect me from other ports being used but I am interested in the port 53 traffic that is trying to be 'hidden' in all the other DNS traffic but goes to its 'own' DNS Servers.)
Any software that plays these games tends to be 'no longer used' !!!