How to SSH into Android from a different network?
Quick answer:

You don't need to 'root' your Android phone - both it and SSH are working correctly.



How to solve problem:

You need to better understand 'port forwarding' and 'public IP addresses'.

The 'port-forwarding' needs to occur where the public network ('Internet') meets the private network (WiFi network with Android device).  This is usually a 'router', but could be a larger 'firewall'.

You need to find out and add this detail, if you want any further help ..