Sometimes the regular instructor is okay with it, and will ask. It might be a fairly routine evaluation (gotta be able to do these 5 things), in which case anyone with enough experience would be okay.I see. In which case I would say this whole situation could have been avoided if he didn't give out those tips. Whenever I cover another teacher's class I don't pass any of the students on any skills or recommend them to be promoted to the next class, as I don't know what standards the other teacher is using to evaluate the students. You avoid a lot of complications that way. Just teach the class and leave the evaluating and promoting to their regular instructor.
It might also be that the CI asked him to do it, to see how he handles the evaluations. It's a useful part of training future instructors.