The man himself answered the question immediately after seeing the aces, "What a fool I am, aces, 1st hand".
Why would the guy 5 bet, shove 1.3 mil more with anything less than aces or kings after being 4 bet? So at best your calling in hopes of chopping.
If Chan had just arrived at the table, even though he probably can look at any stack and get a rough idea, did he even know what was shoved at him, did he add up the numbers, nope, "what a fool I am, aces, 1st hand" Had no identity of the table, I love the guys face and blurt of "I'm all in", like oh well, what the hell, he knows Chan has kings and he knows showing desperateness to a larger stack will get the instacall. And his, what an idiot smirk after hearing the "I call" and confiriming the kings was priceless.
As much as it was poor play by Chan, the body language and tone in the "I'm all in" was well played