An early reference to the expression, which may explain Twain's assertion, is found in a speech made by Leonard H. Courtney, (1832-1918), later Lord Courtney, in New York in 1895:
'After all, facts are facts, and although we may quote one to another with a chuckle the words of the Wise Statesman, "Lies - damn lies - and statistics," still there are some easy figures the simplest must understand, and the astutest cannot wriggle out of.’
There's no indication that by 'Wise Statesman' Courtney was referring to any specific person, although it may be that Twain thought that he meant Disraeli.