It's often said that the angelic interpretation of Gen 6:1-4 represents the traditional interpretation of the text. The most ancient interpretation. Let's consider a statement by Josephus:
For many angels (11) of God accompanied with women, and begat sons that proved unjust, and despisers of all that was good, on account of the confidence they had in their own strength; for the tradition is, that these men did what resembled the acts of those whom the Grecians call giants. Ant. 1.3.1.
What's striking about this statement is the caveat: "for the tradition is…"
That disclaimer seems to distance Josephus from the interpretation he recounts. He shares that interpretation with the reader, without committing himself to it. Indeed, it suggests tactful skepticism on his part.