User blog comment:EmpyreanSmoke/Supernatural Q&A/@comment-4632123-20150922202934/@comment-24834479-20150923000035

1. Either he was granted the title archangels by God (which is less likely), or metatron wanted people to think he was.

2. Castiel absorbed the damage from Sam.

3. They are not cannon.

4. Unsure of this.

5. The human who instantly exploded was too far off from the family line of pure vessels to hold an angel.

6. They are both mutilated souls in different ways (monsters and demons), so I suppose a monster soul could also be twisted into a demonic spirit.