I am bemused when I read articles like this one and find that the author fails to mention or show any awareness of the myth of the watchers and the giants, which is the only account of the origin of demons in Second Temple Judaism (or earlier). See here and here for specifics.
One could answer that the author is writing from a Christian tradition in which the Enochic literature is not part of the authoritative biblical canon.* This is true enough, but even if we stick to the the Protestant biblical canon, there is unsettling evidence that the Enochic literature was not ignored by it. In Jude 14-15 the author (traditionally the brother of Jesus!) says the following:
14 It was of these also that Enoch in the seventh generation from Adam prophesied, saying, “Behold, the Lord came with his holy myriads, 15 to execute judgment on all, and to convict all the ungodly of all their deeds of ungodliness which they have committed in such an ungodly way, and of all the harsh things which ungodly sinners have spoken against him.” (RSV)This is a direct quotation from the Enochic Book of the Watchers (1 Enoch 1:9):
9 And behold! He cometh with ten thousands of His holy onesSo for one New Testament author, the Book of the Watchers — which tells the myth of the watchers, giants, and demons — was "prophecy." I would think its view about the origins of demons was at least worth a mention. But maybe that's just me.
To execute judgement upon all,
And to destroy all the ungodly:
And to convict all flesh
Of all the works of their ungodliness which they have ungodly committed,
And of all the hard things which ungodly sinners have spoken against Him. (Charles translation)
*It is part of the biblical canon, though, in Ethiopic Christianity.