I didn't find anything using that hashtag either, but I'm not super literate with Twitter.
I took a look at Sway Bar (where the event is hosted), Twitter and Facebook for the hashtag and the accounts for Sway and Wendy's and I found... nothing.
Maybe it's just super secret, but it feels a bit odd to me. In my search, I also saw the ad posted on this thread (those three items for £5) and the same identical ad, but those same three items for £4...

Doesn't quite feel right to me so I'm not going to go out of my way for not. I'm also vegetarian and it's not clear of they're a meat-only limited menu for the pop-up.

If anyone does go, let us know if it was real!