Okay. Although at the beginning of the episode when he was on the phone and being told about Nacho's betrayal, the guy said, "We'll soon find out who he works for." So I guess that motivated him to get Mike to plant the evidence - to answer the question of who he works for, then figured they'd kill him after being satisfied by the planted evidence, plus giving Nacho a loaded gun and being told shoot anyone who comes through the door. I guess that makes sense even if Gus obviously misplayed his hand.