Trump's only tweet on the Mayor was, "At least 7 dead and 48 wounded in terror attack and Mayor of London says there is 'no reason to be alarmed.'" The tweet is a one-sentence observation of the irony of the Mayor's statement. Trump did not criticize the Mayor as a person nor criticize the efforts the Mayor was taking.  
The problem with this type of article is that it adds a lot of speculation and emotional baggage to a simple sentence. It is trying to make the situation more than the situation really is.
A less inflammatory article would just provide the tweet and then the Mayor's explanation.