every network adapter has its own unique hardware address, the MAC address. It is globally unique, too.
Whenever a router is connected to by a network adapter and asked to supply an IP address via DHCP it will note the MAC address in its database together with the IP address it supplies to the adapter.
This is in order for it to normally supply the same IP address the next time the same adapter connects.
Now, in your case you have two different network adapters, the WiFi and the Ethernet adapters and they have different MAC addresses. So the router will always supply different IP addresses to them. This is built into the networking system.
In fact the handing out of the same IP address every time an adapter connects is NOT certain, it depends on the router make for how long it will keep the old address memorized, so you might not even get the same address for the WiFi adapter every time.
This can be solved on the router by making what is called a "reservation" in the DHCP server section. A reservation ties together an IP address and a MAC address permanently and is therefore what you should do in your situation to ensure future address changes will not happen.
But WiFi and Ethernet will always get different addresses.