That's his reputation, but it is not entirely correct. He was the Conservative candidate, so he is definitely right wing - and I am not supporting him, just noting that Livingstone's Congestion Charge was among those policies that failed to win over the London electorate.
On the other side, Livingstone was the preferred candidate of the City of London's financial sector, and the Hoxton/Limehouse glitterati for whom he has been working very hard the last ten years, and by no means as radical as painted. His working class support is stronger among immigrants than the white working class. His great weakness, as the vote shows, was that he was the mayor of inner London, not the Greater London suburbs, which weakness Johnson exploited.
Johnson's wife is Indian, and his grandfather Turkish, so he is not a visceral racist. But he certainly shares the casual loathing of the developing world that is so common here. The quote most often used to justify the allegation of racism is this comment, on Tony Blair's visit to the Congo in 2002
"No doubt the AK47s will fall silent and the pangas will stop their hacking of human flesh, and the tribal warriors will all break out in watermelon smiles to see the big white chief touch down in his big white British taxpayer-funded bird."
The passage is supposed to be provocative, but the language used is meant to be a parody of the imperial condescension of Blair's mission to Africa. (The Guardian made a big deal out of this, but the liberal left here call 'racist' more as a substitute for an argument than the making of one.) Of course, Johnson is a master of 'dog whistle' messages, campaigning in inner London as a multi-culturalist and in the suburbs on a 'stop crime' appeal.
A twit? No, I think that is a performance to disarm critics, especially those (many) who find his upper class background wearing (like me).