It was deemed a good thing not to spoil the show because ratings would be higher if non-book readers didn’t know what was going to happen, not because people would cry about a trivial spoiler. Anyone who pays any attention to the show knows Gendry did not die and was not even in peril when he was last seen. It should have been obvious that there was a strong chance the true heir to the Baratheon line would show up again. Even if it wasn’t obvious it hardly ruins the show to simply know he isn’t dead. And again, this was information already in the public domain. It is perfectly fine to talk about generalities that have been known for months. Just like people talked about the fact that Jon Snow wasn’t dead because Kit Harrington was seen on location. That isn’t a spoiler several months later.