It's entirely possible to simply not follow modern music or celebrity culture enough to recognize a big time singer when you see one.
How in the world can I be expected to know what Ed Sheeran looks like if my exposure to pop culture is limited? The majority of my internet time is spent on GAF, my Youtube subscriptions, educational resources, and stuff I need to google. I'm pretty sure I've seen some sort of video of Ed Sheeran before, maybe a couple of years ago. I guess his face wasn't memorable. I must have heard him since then without realizing who he was.
I watch a ton of movies and shows, I play a couple of games at a time, I read my Kindle a lot. I don't have cable or satellite TV. I have no idea what's trending on Facebook, Twitter, or Youtube's front page. I despise stupid celebrity obsessed magazines and gossip sites. I don't even listen to the radio or Spotify very often. I mean, I didn't even know the Kardashians were a thing until they'd been in the spotlight for 3 or 4 years and it was finally brought to my attention that Keeping Up with the Kardashians was some huge show.
So yeah, it's not necessarily some grand act of edgelording to say you didn't notice Ed Sheeran in his Game of Thrones scene.