Just clicked on that Tweet to peek at the comments. Bit surprised there's a few saying, Why aren't the Royal Family leaking it/where is the video?I got some tea, I promise not to throw it on you
Assuming the video exists and it's not a false flag - Meghan is (apparently) saying she has all sorts of things documented (about the racism accusation), this may be them saying, We have things documented too. It could be used as a bargaining tool to stop her escalating things further.
One Tweet replying says they read a Tumblr post saying a security guard videoed it.
As someone pointed out (somewhere elsewhere on the 'net) the Royal Family don't behave like Hollywood - they prefer to do things as stealthily as possible.