alt Hacker NewsThis is also not true and hasn't been so for years. One can set a preference to "not recommend", but one can not explicitly block any channel.
Depending on your particular "preference constellation's weights" (over which you have no direct control), you can, in fact, be shown videos from that channel again.
Or they just launch another channel. I've had to block about a dozen channels by that bald bearded guy with the glasses.