It was neither a mistaken perception or an illusion.
Joshua's senses definitely would not be wrong.
As a being who had battled against the Ultimate Sublimator Collective and defeated it, Joshua had gained significantly from that violent battle. Be it his deft application of various Extraordinary powers or probability projection towards the future, everything had been honed to complete perfection in the terrible conflict.
At present, the warrior now possessed every form of supernatural power including Psi, magic, lifeforce, elements, ether, Holy Light, and Shadow regardless of type—it would certainly be true that he frequently used Steel Strength, a variant of lifeforce, but that did not mean that he could only use that one ability. As he was now, Joshua was a master of all trades, and could confidently apply magic or indeed the Holy Light.