Two possibilities. (1) Either the policy actually excluded airframe damage caused by an engine malfunction (which would be unusual in my experience, but I can't rule it out), and they therefore had every right to deny coverage, or (2) they unscrupulously put one over on you. Without the policy, or their correspondence denying coverage, we really can't know the answer.
You would be incorrect. I mean, I can't recite it from memory, but I know what it does and doesn't cover.
Wholeheartedly agree on both.