What could have caused an electrical shock from a concrete patio?
Cement is not a good conductor so a live electrical charge from the cement is a near impossibility.  But that doesn't rule out a static charge.  If the humidity was right and enough friction from the wood to break some electrons free just might generate a static charge.  But I have never heard of cement getting a static charge before but then again, I'm not moving wood a lot on a cement pad.