I don't think Now and Later was being completely disingenuous just repeating a “fact” from the apologist mantra, one made up from a bit of twisting of the real truth.
In specification saying the Jews of the Old Testament as a religion were henotheistic is not quite accurate.
The truth that forms the basis of the LDS “facts” in this regard is that there were factions among the Israelites that recognized other gods. Some were even polytheistic to at least some degree. The false idols and such in the Movie Ten Commandments for example point this out. For lack of a better way of putting it some were not as 'Jewish" as others, there were not following the Jewish faith as it really was but adding things from other cultures that they arose from or were exposed to as they saw fit. Sounds familiar...
Anyways, it did not help that definitive law was still not quite in place yet.
The Burning Bush rapidly brought these practices to an end.
Digest this book (one of many), from the impeccable Old Testament scholar, Margeret Barker. She’s has written several books on the era of 2nd Temple Judaism. The theological construct sounds strikingly like Mormonism, it ain’t funny.
http://www.margaretbarker.com/Publications/GreatAngel.htm
“Many of the old certainties have been destroyed by new knowledge. What has become clear to me time and time again is that the evidence indicates that pre-Christian Judaism was not monotheistic in the sense that we use that word. Many in first century Palestine retained a world view derived from the more ancient religion of Israel, in which there was a High God and several Sons of God, one of whom was Yahweh, the Holy One of Israel. Yahweh the Lord could be manifested on earth in human form, as an angel, or in the Davidic king. It was as a manifestation of Yahweh, the Son of God, that Jesus was acknowledged as Son of God, Messiah and Lord.”