Blossom out

When a village idiot blossomed out all of a sudden in new clothes, the neighbors wondered at his prosperity.
"What's happened to you ?" asked one of them.
"I won the first prize in the lottery," he answered.
"How did you come to guess the lucky number ?"
"Well, three times running I dreamed of seven ; so I figured it out that three times seven is twenty-four, and I bought ticket number 24. I won the first prize."
"Why, you fool, three times seven is twenty-one, not twenty-four."
"Is that so ?" said the village idiot. "Well, twenty-four won, anyway."

1. Could you tell me what "blossom out in new clothes" means?

2. Does "wonder at his prosperity" mean "wonder why he was so successful"?