no, they did not come up with it later.
insane amounts of money was being invested into quantum computing far before Bitcoin existed. Shor discussing his algorithm for factoring cryptographic keys in the context of quantum dates back to the mid nineties. The first demonstration of an actual physical implementation of quantum was over a decade before Bitcoin, and it was for search regardless, not breaking signatures. The whole universe does not revolve around Bitcoin and all of this work began a couple decades before the genesis block.
