People can use the numbers behind the chart to argue in whichever direction they'd like to. Michael Mann leaves himself an out in case he's wrong in his email's second point:
"Michael Mann, a climate scientist at the University of Pennsylvania who is
known for his analyses of past global temperatures, said he was also surprised by the suggestion that the planet got so warm.
[1] The finding supports many scientists’ concern that
feedback loops in the Earth system could lead to much higher temperatures than most climate models predict, he wrote in an email.
[2] But it’s also possible that the data assimilation assumes too much warming and is missing factors that might forestall a runaway greenhouse effect."