It appeared on the official Twitter account of the Chinese Embassy in Ireland.
The account shared a Tweet by the PM referencing the 25th anniversary of the handover of Hong Kong to China.
The PM’s Tweet included a video of Mr Johnson and the words: “25 years ago we made a promise to the people of Hong Kong. We intend to keep it.”
The Chinese Embassy in Ireland retweeted the post but added: "2 years ago we made a promise to the Northern Ireland Protocol. We are determined to break it.”
That is a reference to the Northern Ireland Protocol Bill, which seeks to override parts of the UK-EU trade deal agreed 18 months ago.
MPs voted earlier this week to give the Bill a second reading.
It comes after the DUP said it will not nominate ministers to allow a new Stormont Executive to be formed until the UK takes actions on its concerns around the protocol, and how it is impacting on Northern Ireland.
However the move by the UK has been branded as illegal and a clear breach of international law.
Friday marked the 25th anniversary of the Hong Kong handover - the formal passing of authority over the territory of the then colony from the UK to China. It ended 156 years of British rule in the former colony.
Under the "one country two systems” terms of the handover, Hong Kong is supposed to be governed in a way that gives it a high degree of autonomy and protects freedom of speech and assembly, and other rights not found in mainland China.
But in recent years China has been criticised for increasing its control of Hong Kong and enacting laws and reforms that stifle free speech and dissent.
Mr Johnson said on Friday: "We're not giving up on Hong Kong.
"Twenty-five years ago we made a promise to the territory and its people and we intend to keep it, doing all we can to hold China to its commitments so that Hong Kong is once again run by the people of Hong Kong, for the people of Hong Kong."