Everybody was born equal.这个句子是被动语态,（每个人生来都是平等的）,可以理解为一个谚语之类的,Every human being was born equal,都是一样的用法,后面的形容词是做表语.
He came to school upset.这个句子用完整的表述式应该是He came to school with an upset mood.后面省略了“心情”.