The power of K3s

[Defendant]

So, I was playing a SnG on pokerroom, 15-30 blinds, mid position, I get dealt AQo. One raise in front of me to 150, so I call and a guy behind me calls as well. Flop is As8s3h. One check, so I raise 450, size of the pot. The guy behind me calls. Next card is the Qd, so I push him all in for 800 more. He calls and...flips over Ks3s.

And rivers a 3d.

WHAT THE FUCK??????

First of all, who calls a 5 big blind raise with K3s???

I guess his call on the flop is questionable but oh well.

But the ALL IN when he misses on the turn???? WTF????

Defendant