Killer Kross was attacking Pagano at the AAA Guerra de Titanes event before he was saved by none other than Sin Cara. Sin Cara fended off Killer Kross and then cut a promo that he was there to save his friend, Pagano.
Sin Cara, whose real name is Jorge Arias, was recently released from WWE alongside Luke Harper and The Ascension. In Sin Cara's case, he had actually rejected being moved to 205 Live before being given his release. Sportskeeda's Tom Colohue said that,
"Sin Cara was one who was asked to go to 205 Live at some point and he declined, so he was shifted from RAW to SmackDown to RAW to SmackDown. It was difficult with a number of injuries, a couple of botches which stood out, from there on it was writing on the wall stuff. I think the release is probably the best call. I don't think Sin Cara really fits the aesthetic of the WWE at the moment, but I can say that about a few more, of course."
It should be noted that, according to WON, WWE has a trademark for the Sin Cara name in Mexico. It's very possible that Arias got permission from WWE to use it, but that's only speculation at this point.