Long, long ago the redwood grew in the Arctic, just as big and tall as they are today.

请问原句是由非限制性定语从句“Long, long ago the redwood grew in the Arctic, which were just as big and tall as they are today.” 演变而来的吗？

这部分“just as big and tall as they are today”是形容词短语作非限制性定语吗？正确的语法称呼是什么？

谢谢老师。