James Dashner is a sci-fi author, perhaps that's where they heard it.
Dashiell Hammet wrote hard-boiled detective stories like Raymond Chandler, he actually introduced the world to Sam Spade.
I prefer Dashiell to Dashner. Dashner sounds (a) like a reindeer, (b) dashner through the snow..... (c) like 'dacha' in Russian, which is a country house, (d) pretentious!
If they're going to shorten it to Dash, or Dashy, it'll sound ridiculous.
But, hey ho, it might suit hem as a couple and suit their little boy to a T. How many parents loved X-Files and named their ds Fox??
Actually, yhe more I hear Dashner, the more it grows on me 
I had Wolfgang on my shortlist for DS but DH vetoed. 'Wolfy' sounds adorable for a baby, perhaps not for a high court judge (etc).