The Hobbit: Battle of Five Armies

If the dwarves only answered the call of the bearer of the King’s Jewel, why did Dain Ironfoot come to Erebor?

Even if he believed Thorin and Company that Smaug was dead, you’d think he’d want proof. Isn’t skepticism the hallmark of the dwarves? Also, mind, he would have had to have left the Iron Hills when Thorin didn’t have the Arkenstone.