How do switches route ethernet packets…
Switches (bridges) do not route packets. Routers route packets. Switches bridge frames. A layer-3 packet is the payload of a layer-2 frame.
Switches are layer-2 devices that are bridges that bridge layer-2 frames between links. When a switch receives a frame on a link, it puts the source MAC address and port on which it received the frame into its CAM (Mac address) table, then it looks up the destination MAC address in the table and forwards the frame to the port associated with that MAC address. If it does not find the destination MAC address in the table, it floods the frame to all ports other than the one on which it was received.
A port can have multiple MAC addresses associated with it in the table because the table is indexed by MAC address, not by port. Multiple MAC addresses in the table can have the same port number. You get that when you have a switch-to-switch connections. The port to the other switch will probably be associated with many MAC addresses.