Slaine said "I FOUND HER!" on the radio. Thus Inaho realised he helped the terrans before he knew the princess was there.
Edited for clarity
The fact he was looking for the princess and attacked/helped to kill a knight should make it obvious he's not the enemy. Now add in the fact he would undoubtedly have to get out of his to see her, there would have been no issue to restrain him and guarantee the princess' safety. Hell, he could've been set up to communicate by video or whatever.
Inaho is up to something the stoic dickbag.