User blog comment:EmpyreanSmoke/How did Cas survive the fall?/@comment-11331875-20150711011429/@comment-11331875-20150711020419

If it wasn't metaphor, then it was a mistake or a retcon. After Metatron took Castiel's grace and finished talking to him, he touched Castiel's forehead and transported him to Earth. Castiel was (utterly unharmed) on Earth and watching as all the other angels fall to Earth because of the spell; he was not among them, ergo he didn't literally fall to Earth like the rest.