I have never seen angelfish eggs bunch up like that, so I would tend to agree that they were cory eggs. As far as angelfish are concerned, sometimes after laying the eggs, the parents may decide to move them (or the developing fry) to a safer location. It happens to me all the time, especially in a community tank or if a tank is located in a high traffic area. Therefore, if the eggs or fry disappear from the original spawning location, look carefully to make sure they weren't just moved before you give up on them. If they are moved, one or both of the parents will still be nearby tending to them, so that would help tip you off.