I manage several websites. When we block an individual IP address, that is what the person at that IP address sees when they try to access the page.
We block IP addresses when we believe that it is a scraper or other type of malicious bot. Maybe there was some behavior from your router's IP address that made them think this. Maybe they just don't like you
Maybe it was a mistake.
In any case, contact the webmaster of the site for an answer.