Truly an odd incident. I can't recall seeing anything like this. Very different from the Aloha accident, as it seems like a "panel" was removed, rather than a structural failure due to repeated pressurization. Every once in a while, you hear of a cargo door or something "blowing off," but this one is obviously different.

While it seems like it's not that wi-fi antenna, a logical guess is that there is "something" attached there that was improperly secured.