Well, for a certain definition of 'human performance'... I believe that's carried over from the DQN paper and is something like 'an ordinary video game player given a few hours'. When it comes to ALE you should usually treat the 'human performance' numbers as being lower bounds.

(In this case, if an agent can beat 'human performance' by only clearing 1 of 9 total levels, one is entitled to a little skepticism about how useful 'human performance' is as a benchmark for this particular game. Focus on the improvement over other DRL agents, not that.)