If you want both subnets to cross communicate fully then yes, you would just ensure you have a static route from Router 1's LAN to Router 2's LAN. This would be created on Router 2's routing table where the automatically created route from Router 2's LAN to Router 1's LAN is.
No, you're not going crazy and I've already had my how-to guide edited to reflect the correct information. Sorry about the confusion, that was entirely my fault.
Start by setting up Router 1 which will be connected to the internet. Then, as per my guide (now revised.....lol) connect Router 2 using the "LAN port to WAN port" method for a separate subnet. As per the guide, and your own experience, Router 2 will automatically create a route between it's subnet and the LAN subnet on Router 1.
Now do the same with Router 3 giving it it's own unique subnet
LAN IP: 192.168.1.1
LAN IP: 192.168.2.1
LAN IP: 192.168.3.1
Both 2 and 3's LAN's will be able to communicate with Router 1's LAN, giving them internet access. As long as there are no routers from Router 1's LAN to their own, they won't be able to communicate with each other.
Which is to say:
Router 2 should not have a route like this: 192.168.1.0/24 >> 192.168.2.0/24
and Router 3 should not have a route like this: 192.168.1.0/24 >> 192.168.3.0/24
To test, get a client on Router 2's LAN to attempt to ping a client on Router 3's LAN and vice versa. If they communicate, then you have a return route from Router 1's LAN to both Router 2 and 3's LAN and you need to get rid of it.
To the best of my knowledge, there shouldn't be. As far as I know, Router's 2 and 3 will only create (automatically) the static routes from Router 1's LAN to their own.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.