fairest way to handle situation?

[fslexcduck]

i won't reveal what the floor decision was until later in order not to skew results. i just want to see how you would rule. here's the situation:

2/5nl, button raises to 25, 4 calls. flop is J55hh. check, mp bets 30, CO calls, button makes it 330, SB shoves for 675, CO calls all in for 300, and button starts thinking. CO then randomly flips over his J5 for the flopped boat, so button mucks his AQhh. SB had 45s and is livid because the flush draw will obviously not call an all in for 375 more getting even money, however he would have called getting 5 to 1 or so not knowing that someone was already full.

what's the ruling here on CO's hand, the situation, etc?