Well, in this case there's no reason to discuss that engine and the "wrong" assumption that it's a clone that isn't allowed to be discussed here not really doing any damage.

So the simple rule may be wrong in single cases, but after all it's a good way to get a quick answer.

In any field, people will reverse engineer the best products and generate derivative works. In this sense, there are no original chess engines, only some engines which have some new features, and some that don't. After fruit came out, all succeeding top engines, including Rybka, used ideas from it. Now that Rybka has been reverse engineered, all succeeding top engines will use its ideas. This will be true regardless of whether the people who put out the engine don't hide their origin and make fun out of it, by using ridiculous names for the authors and using fish graphics and so on. Simultaneously they say "oh, btw., it's no clone", what some naive people use as "look, they say it's no clone".

As with any other product, the only way to combat this is with continuous product improvement. Without this, someone in the community will pick up the reverse engineering work, improve it, and come out with a product that is more useful than the original. In my opinion, this has already happened in the case of Rybka and its use for analysis, where other engines support basic functionality like MPV and constrained branching factors that Rybka lacks.