Illegal, where exactly? In various western countries ISPs are by law required to block some websites. In other countries, ISPs ar eby law required to have escape hatches to be able to shut down the internet. In yet others, everything runs behind a firewall. Take your pick, I guess?

Very few, if any, countries makes this illegal.

Some countries have laws around Net Neutrality or Open Internet that can protect you from this, but even those countries have other legislations that can superseed that in specific cases. (e.g. hijacking DNS can be completely legal for some child protection laws, or to uphold laws that makes some web sites illegal)

The hijack is probably legally mandated. The site he was trying to reach is a torrent site.