How does Gandalf prove to be a great manipulator when he was talking to Beorn?

Gandalf told his story amidst distractions and interruptions, all of which proved to make Beorn more curious. Thus, because he was interested, he neglected to send the dwarves away..... Beorn had few friends and didn't like company. Gandalf worked past Beorn's suspicions.

"Well, now there are fifteen of you; and since goblins can count, I suppose that is all that there were up the trees. Now perhaps we can finish this story without any more interruptions." Mr. Baggins saw then how clever Gandalf had been. The interruptions had really made Beorn more interested in the story, and the story had kept him from sending the dwarves off at once like suspicious beggars. He never invited people into his house, if he could help it. He had very few friends and they lived a good way away; and he never invited more than a couple of these to his house at a time. Now he had got fifteen strangers sitting in his porch!