What does the gematriya scene suggest about the character and authority of Reb Saunders? What is the origin of gematriya?

Reb Saunders application of gematriya (at least in this instance) represents a deliberate error. He is testing Danny's attentiveness and wit, doing so in an incredibly stressful manner. If anything is clear, it is that Reb Saunders is more than willing to put his son through a very rigorous public process without a consideration for his "image" or self-confidence.