From legal point of view ... I think you should obey whatever BYOD policy states. IT department knows which parts of their network are more secure and which are less secure. If desired access method for BYOD devices is not explicitly mentioned in BYOD policy then I would say that IT department needs to improve communication with employees. You don't have to figure out on your own which parts are secure and which are not. Also, if IT department is smart enough they could automatically enforce this "legal requirement" by configuring their Ethernet switches to drop traffic from unknown source MAC addresses as first layer of defense to prevent accidental BYOD policy violations (of course MAC address can be changed, but this would imply that you know what you are doing).
From technical point of view ... Authentication and Internet Packet filtering security could be implemented differently for wireless and wired access methods. This means that sometimes Wireless access method could be safer (for example, if over wireless you are required to use VPN Gateway that can filter all unwanted traffic and run anti-virus "in the cloud"). However, sometimes wireless can be less secure if they don't have VPN gateway and solely depend on WiFi authentication that is unsafe. There are other variables that could effect security, but it is hard to judge without knowing how network is configured in your company. Where I am going with this is that, if your company has reasonable upper-management you could try to escalate this issue to them. However, you will need to argue from security point of view why you are right and network admin is not. This would require you to understand how IT department has wired up network in your company.
From relationship point of view ... As another person pointed out in a comment, sometimes it is better to apologize and say that you did not know about this BYOD requirement. You have to understand that network admin and you will be working in the same company for some time. You don't know when your paths will cross again.
Also, I would be really careful about disclosing too much information about your company's IT configuration publicly.