scotty win ME bustout hand

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i had espn on last night in the background and half way heard the hand scotty busted out on..

he was in BB with AQ vs SB w/ 55.

flop comes Q5x , sb checks, scotty bet, sb call.

turn K, sb checks and scotty goes allin???? wtf. can someone maybe fill me in on stack sizes or do i have the hand wrong?

why would he turn his hand into a bluff here?