The founder of Green Mountain Coffee Roasters Inc., who was ousted as chairman for a stock sale that violated company policy, said the sale was triggered after he was caught off -guard by a swift drop in the coffee maker’s stock price. Robert Stiller, who also has dumped his $50 million stake in Krispy Kreme Doughnuts Inc., said in an interview Wednesday that he didn’t expect Green Mountain’s shares to fall so steeply last week. The decline forced him to sell the shares on a margin call, but it occurred during a blackout period in which the company prohibits the sale of its stock by insiders.