He said thank you, for allowing him to see the anarchy that exist outside of the gates of Alexandria. The weirdest part of the “Thank You” was it highlighted just how selfish and pointless Nicholas’s contribution was both to Alexandria, pre-Rick and gang, as well as afterward. Nicholas, if you watched last night knifed a zombie, who had been a member of one of the rescue crew. In a way, the “Thank You” was an insincere thank you, given that Nicholas’s last act killed one of the best characters, Glenn, and made him suffering, guts ripped apart and so forth, just so that Nicholas could shoot himself in the head, perhaps the most selfish act imaginable in the Walking Dead World.