You may have misunderstood. One of the things contained in the 'status' message is the router's WAN IP address. In some cases it could be possible to say which interface is in use by looking at the IP address.
For example, if you are that your wired WAN network is 192.168.2.0/24 and the 'status' message returns WAN IP as something like 192.168.2.122 - then it's wired. If the message returns an IP from another subnet, like 10.160.0.89 - then it's possibly mobile.
This is easy to determine only if you have good knowledge of the networks your router may use, but it doesn't specifically tell you which interface you're using. So in short - there's no direct way.
Though you can add a rule to Status → Events Log → Events Reporting that informs you automatically of which interface is used when they do change: