BFD operates on top of layer-3 and layer-2, so it is not concerned with IP or MAC addressing. In fact, a layer-2 protocol, e.g. PPP, between the routers may not use MAC addresses.
When a router sends BFD, including BFD Echo, to another router, it will use the layer-2 and layer-3 addresses of the other router as the destination layer-2 and layer-3 destination addresses of the frame and packet, respectively, but that really has nothing to do with BFD itself, which, in theory, is independent of the layer-2 and layer-3 protocols used to carry it.
When Router A sends BFD to Router B, it will use Router B's layer-2 address (possibly a MAC address) as the destination layer-2 address, and it will use Router B's IP address as the destination IP address. When Router B sends BFD to Router A, it will use Router A's layer-2 address (possibly a MAC address) as the destination layer-2 address, and it will use Router A's IP address as the destination IP address. It doesn't matter if the BFD sent is a Control or Echo packet. The underlying layer-2 and layer-3 protocols need to use the layer-2 and layer-3 destination addresses of the target router.
For instance, when a host with a web browser sends a request to a web server, the web server replies with the destination address of the requesting host, not its own address. BFD is the same way; it is the payload of the layer-3 protocol, which is the payload of the layer-2 protocol.