It is not unsound that this man believed that God was able to protect him. What was unsound is that he took a Bible verse promising divine protection to believers and mis-applied it, thinking that God would protect him if he foolishly danced with poisonous snakes.
While Jesus was in the wilderness, he was tempted by Satan to display his power as the Son of God in various ways so that the people might believe. But Jesus rejected the method of tempting God by doing outrageous things to attract attention, like falling off the highest point of the Temple and having angels catch him.
As a Christian, I believe that God is sovereign and, in the words of the Apostle Paul, “that for those who love God all things work together for good, for those who are called according to his purpose” (Romans 8:28). God has given us certain promises in his word. These can be relied on, but they are not the sum and substance of our faith. As Christians, we shouldn’t haven’t to get bitten by venomous snakes and live in order to know that God’s word is true. In the words of Paul, “For all the promises of God find their Yes in him” (2 Corinthians 20). I put my trust in Jesus, and at the end of the day that is all I can do.