Why didn't I strike Bluhz first since he walked into me?

civilized <0hp 0m 0mv 8332tnl (45.18%) 10 PM> where
People near you:
(PK) Bluhz Approaching a Large Crossroads
Kalyden A Large Crossroads
(PK) Ishuntal Approaching a Large Crossroads

civilized <0hp 0m 0mv 8332tnl (45.18%) 10 PM>
Bluhz has arrived.
A savage orc has arrived.
MORE BLOOD! MORE BLOOD! MORE BLOOD!!!
A savage orc yells 'Help! I am being attacked by Ishuntal!'
Your punch DISMEMBERS a savage orc!
A savage orc is writhing in agony.

civilized <0hp 0m 0mv 8332tnl (45.18%) 10 PM>
Someone runs past you and suddenly your legs are swept from beneath you!
Adili steps out of the shadows.
Adili's trip scratches you.
You dimly note through your hazy senses that you are being attacked.
Bluhz gets a wild look in his eyes.
A savage orc is writhing in agony.

Bloodthirst check occurs on a pulse, not when someone enters the room. So Bluhz arrived, then the orc arrived, the orc is 'on top of the stack' of people in the room (since he entered last) then the pulse happens, you attack the orc.