Balance
Rui wasn't sure what was happening. He didn't understand how this was possible.
How was the symbiote, assuming that's what the shadow clone of himself was a manifestation of, able to gain access to his techniques? Not just his Martial Art techniques, but also the VOID algorithm. The movements that his shadow clone-self had displayed were without a doubt the VOID algorithm, the movement used was the perfect counter to his movement and it had been initiated even before his own.
That was the classic tell-tale sign of a perfectly executed VOID algorithm adaptation via the pattern adaptation system of the VOID algorithm. The shadow clone was clearly using it, as well as other techniques.