My 2 Cents, it is thought that Angels, Demons and the satan etc only entered Israelite/Jewish religious thought during the Babylonian Exile, so the references would have been written after 539 BCE, and edited in to any texts used that were earlier.
So, as the new ideas were that, very new, it is perhaps no surprise that "Angel" is used that way of Yahweh , as he was a god alongside other gods for so many Centuries before the Exile, even if at the time assimilating into himself those other gods. But the returnees were only working toward monotheism, and were still monolatrous, so here in these examples you give we see examples of the slow changes in thought taking place.
I guess even in Christianity Angels are really seen as nothing so very different from that early concept, as they are seen as demi-gods, not just messengers, but powerful beings fighting battles alongside Christ.