Nah, I hadn't really thought it through that much, and was just generally pointing out my thoughts on eyecandy being just one of many features a levelmaker can use to brew something special.

From what I've learnt, eyecandy can be anything that makes a level look more alive while not directly affecting gameplay. It could be categorized into 'layer 5' background and foliage, with the latter blending in with the foreground (layer 4) most of the time.

And I agree that there should be a clear difference between foreground and background you cannot interact with. There are even newer games that got it wrong every here and there. In Ori And The Blind Forest for example, I once died by jumping on a rock that was in the background, and walked in a lava stream that looked part of the other lava streams in the back, but wasn't..