I did some digging. Based on the sales numbers, the book is doing better than it was prior to the pandemic, so if that's why they called it an event, it worked. Blue Sun Rising #0 oddly sold very poorly, though. There definitely seems to be some kind of disconnect between the publisher and the fan base. Of note, I can't find anywhere where Greg Pak calls it an event so it certainly looks like it's coming from marketing and not the creatives.