In one of the climactic scenes of No Country for Old Men we see Sheriff Bell arrive at Llewellyn's final hotel room. Inside we see Chigurh armed with his silenced shotgun, Bell noticed the door lock and realising that the man he was chasing the whole time was on the other side of the door, pulled out his weapon for the first time (after going unarmed the whole film). When Bell enters, we see that Chigurh has fled out a bathroom window with the cash he took from the vent (a detail Bell noticed).
My question is, why did Chigurh flee? Why didn't he kill/confront Bell like every other character he had faced? (Excluding the shop clerk and fat lady)