IP Blocked

This is a bit confusing, you do need a public IP address to connect to the www. I don't have a static public IP address, I think it has a lease of a week or something. My WiFi is not hacked, I look every now and then on my router.

Public IP's are the ones that the rest of the world can connect to, like youtube, this forum, etc.
Private IP's do not get routed to WAN, they are used only inside LAN.
If you are not on a public IP, no need to worry, probably was blocked due to someone from the same ISP as yours.
There is also the possibility of someone half way around the world using a VPN or TOR that goes out from your ISP.

Not sure what you mean with being on a public IP. My modem receives a IP address from the ISP, that's a public IP (WAN address), without a public IP I wouldn't get a connection to the www. If someone could connect to it depends on if there is a port routed to a service which the client could connect to. My machines got of course private IP addresses provided by the router with a firewall (local network). If I would have the public IP on my machine (possible by bridging the modem/router), only that machine would have internet unless that machine should be configured as a router.
I'm not worried, but it's a bit annoying to need to workaround the IP block. Public IP addresses are unique, when I connect to www.linuxcnc.org it's my (public) IP that gets routed to the server of the web host of linuxcnc.org.
Although I'm not blocked anymore at the moment I still suspect there is something off with the configuration of the IP block tool.

The IP address may not be blocked by Linuxcnc. 

If  spam is detected sometimes the blacklist servers will block a whole address block.
In one instance a whole class C address block was blocked for one spammer. Thats 4 billion IP addresses. Very lazy work on behalf of the blacklist server. Then its up to the ISP to demonstrate it should be unblocked.
 

Ah that makes sense, hopefully this is incidental and not so many people who suffer from it. Otherwise it might be a good idea to check if it could be set a bit less aggressive/rigorous.

Every time an IP is blocked temporally it's always been 5 attempts in a few seconds so it's a seasoned hacker for sure.

JT