__ his fluent English, he must __ in America for a long time

__ his fluent English, he must __ in America for a long time.
judged by...have stayed...
judging from...have stayed
为啥答案选judging from那个？？主句是he，he不是被判断吗？？不是应该judged by被动的吗？？而且不是有一句“We couldn't judge one person by his appearance.”吗？？不是应该judge by才是固定搭配吗？？