Sure you can argue that. But any App Promotion App is ultimately downloaded from the App Store originally, so I'd assume it's reasonably obvious. But even so, I don't think that Apple's adding a specific clause to their App guidelines due to the very small percentage of people who are downloaded App Discovery apps and then get confused.

If I had to guess at their motivation, it would be their attempt at blocking paid-for-promotion schemes that try to game the App Store ranking systems. I think that's more likely.