No, just uninformed.
It is quite possible that the agents know less about Mileage Plus than the passengers. After all, they are "two separate companies"
Of course this is a shortcoming which should not be allowed to exist, but you have two options to protect yourself from misinformation:

1. Check in with FlyerTalk and get what is more likely to be the correct information
2. Hang up, call again. Some say 2 out of 3 is enough to be fairly confident you've gotten the right answer. Me, I prefer best 3 out of 5, or stop and get somebody's name when I have the answer I like.

But don't worry, it's very unlikely they were intentionally trying to give you the runaround.