I cannot tell you that that is what happened. All I can say is that it is possible. There is a very common electronic component known as a capacitor, one purpose of which is to store energy. It is constructed of parallel metal plates separated by a material that does not conduct electricity. So the charge that builds up on one plate cannot travel through that material and reach the other plate. If you touch its two wires together, current will flow from one plate to the other through the connected wires. That current will continue to flow until the charge has completely discharged from the plates, a matter of milliseconds in duration. Your deck with its metal parts and the dirt below the deck could constitute a similar set of parallel plates. The lightning could impose a charge on this “make shift capacitor,” and a person touching the metal part of the deck could act the same as the two wires of a capacitor being connected to each other.