This was just information for you, it isn't likely to be the cause of the URL Blacklist (just advice, act on it as you see fit). URL blacklist can occur for various reasons, a 3rd party link to a site on the blacklist or if the domain is on a shared IP address, it could be a domain/url on that IP address.
Only the Avast virus labs team can review and remove the blockage if they determine it is an FP or not. That is why I gave you the link.