finished可以是形容词，用作表语，意义之一为：having reached the end of an activity, job, etc.
He started his homework two hours ago and he still isn't finished.
I'll wait here until you're finished.
所以，网友的第一个句子为主系表结构，形容词作表语，意为完成了，干完了，做完了。第二个句子为动词finish的现在完成时。二个句子表示的意思是很接近的, 类似于：He is gone. He has gone.
