I checked all his tweets on June 11th, and none of them mentioned any statues in the UK. What's more, the two tweets in question immediately follow his (quite accurate) insult of Trump.

Don't get me wrong - the UK did lead the way when it came to getting rid of slavery in Europe...though they certainly still had feet of clay by having colonies that had slaves for decades after it was banned in the UK itself, not to mention their actions in India and in China (the Opium Wars).

That being said, all nations have feet of clay, and when it comes to her time as the dominant power, the UK's actions were certainly better than most.