Awesome! Glad to hear it!
In order to create a unique network that is separate from another, it has to be defined with a different subnet.
Each subnet operates at layer 2 (L2) -- switching. Basically this is how devices on the same network are able to communicate with each other with MAC address level connections. This only allows devices on the same subnet to communicate with each other -- it doesn't have the capability to route from one network to the next.
Routing is a layer 3 concept and allows different networks to interact with each other (if permitted by firewall rules) using IP addresses. In order to route, there must be different subnet on each side of the routing engine. If you have 2 networks that have the same subnet definition, there would be ambiguity about where a packet should go and the router would not know how to route packets. Let's say that Bob, Bob, and John are sitting together at a table and John picks up a package from the desk that is labeled "Bob" -- which Bob does he give it to? If, on the other hand, it is Bob, David, and John, there would be no ambiguity that the package labeled Bob goes to Bob -- the only Bob in the room.
Masquerading is concept of "hiding" or "masking" a network behind a single address. In IPv4, this is totally common for home connections -- your ISP gives you one IPv4 address, and your router performs NAT (Network Address Translation) Masquerading to create a private network that can share many devices with just a single ISP provided IP address. It's like how an apartment building has a single street address, but many people live inside. This is necessary on your lan zone in this case because the Pi takes one IPv4 address on your main LAN and then creates a network behind that (via NAT Masquerading / routing). It is possible to not use masquerading -- that requires that your upstream router has a feature to add static routes. But that's another technique entirely and not necessary for most guest network type configs.
In the meantime:
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