VM Guest getting assigned same IP as host when using bridge adapter

You attached the virtual machine to a Wi-Fi adapter. Regardless of what bridging method you use – Windows-provided or VirtualBox-provided (your screenshot shows both in use simultaneously) – trying to bridge Wi-Fi will cause the same general problem: It does not allow the host to lie about its MAC address.

Even though the virtual machine thinks it has its own MAC address, the host bridge has to quietly rewrite it on all outgoing packets (thus implementing "layer 2 NAT" or "arpnat"). This is needed because the Wi-Fi frame headers require the radio transmitter to identify itself, and don't allow clients (stations) to fill in a source address different from the transmitter's.

(Ethernet does not have this problem. Wi-Fi has an optional mode which solves the problem, called "4addr" aka "WDS bridge", but both the client and AP must support it.)

The end result, as @FrankThomas noted, is that your router (DHCP server) sees the same MAC requesting addresses both times. Depending on the router's configuration (e.g. static reservation or out of spite), it might always offer the same address for the same MAC.

(Yes, DHCP requests carry their own copy of the source MAC, independently from the L2 header... but I seem to remember that at least VirtualBox's arpnat implementation rewrites that as well. I'm not entirely sure.)

If you indeed have static DHCP leases, one possible solution would be to bind them to the "Client ID" instead of the MAC address. A standards-compliant DHCP server must distinguish between requests with different Client IDs, even if they come from the same MAC address. (And vice versa, the same "Client ID" must be associated with the same lease even if the MAC address is different.)