Some Champions from the Shadow Isles attended the Bloodmoon Festival

I don't know why but, I'm not saying that I believe or not but, was it actually true that Kalista, Thresh, and Elise were apart of the Bloodmoon Festival because, I'm curious on what they were doing there it gets me really confused since, the only Champions I've heard that were apart of the Bloodmoon were Akali and Shen.

Can someone tell how Kalista, Thresh, and Elise were apart of the Bloodmoon Festival?