Maybe the question is why is the palace telling Rebecca English to inform us that MM is not in Canada, when no one knew or even wondered or cared for that matter. Instead it's just creating a confusion as to what ABC is saying. Maybe that was the point. To create chaos.
No, that point is easily answered. Someone had apparently seen her on an Air Canada flight and it was picked up by a gossip blogger. Speculation ensued. Journalists will have been contacting Kensington Palace and asking them: “Is the Duchess in Canada?”. The Palace responds “No, she’s not in Canada, or LA either, and no plans to be there in the near future”. The journalists pass that onto their readers (e.g. Rebecca English’s tweet.
That much is covered in what I posted on the first page of this thread. As ro why KP said no she’s not in Canada, the most likely reason for that is because Meghan asked them to, because her trip was private (and she has a right to a private life).
As to how Omid later came to tweet about her trip, well, once news of the trip remained secret information, it became a commodity, and could then be given to a journalist as an exclusive for whatever reason suited Meghan. We saw this play out in the texts between Meghan and Jason Knauf - she said that if she was happy with the proposal for his book, she would invite him along to an engagement she had planned.