Yes, that passage is the start of the argument against the "scientists." But before the explanation of what should be accepted as "natural" is given, the matter is connected to the role of convention:
[890a] is at that time authoritative, though it owes its existence to art and the laws, and not in any way to nature. All these, my friends, are views which young people imbibe from men of science, both prose-writers and poets, who maintain that the height of justice is to succeed by force; whence it comes that the young people are afflicted with a plague of impiety, as though the gods were not such as the law commands us to conceive them; and, because of this, factions also arise, when these teachers attract them towards the life that is right “according to nature,” which consists in being master over the rest in reality, instead of being a slave to others according to legal convention. — Plato, Laws 890,translated by R.G. Bury
The matter of nature versus convention is being directly connected to a discussion of who is above the law. That certainly did not come up when I studied the behavior of fruit flies. It involves other issues than a person believing or not believing in a divine agent. The next statement from the Athenian brings in a tiny bit of Socratic persuasion while considering proper punishment for the crime:
What, then, do you think the lawgiver ought to do, seeing that these people have been armed in this way for a long time past? Should he merely stand up in the city and threaten all the people that unless they affirm that the gods exist and conceive them in their minds to be such as the law maintains2 and so likewise with regard to the beautiful and the just and all the greatest things, [890c] as many as relate to virtue and vice, that they must regard and perform these in the way prescribed by the lawgiver in his writings; and that whosoever fails to show himself obedient to the laws must either be put to death or else be punished, in one case by stripes and imprisonment, in another by degradation, in others by poverty and exile? But as to persuasion, should the lawgiver, while enacting the people's laws, refuse to blend any persuasion with his statements, and thus tame them so far as possible? [890d] — Ibid
The Dialogues challenge us to ask how much to accept or question convention while seeking the actual Good rather than poor copies of it. The distance between that openness to discover what is not known and this argument for the gods upon the basis of service is large.
I spoke too broadly when saying the account of soul in the Laws did not fit the story of the Timaeus. It is an edited version of some details to serve a rhetorical purpose. Regarding how to view "materialism" versus "form" there is this observation:
Athenian: The sun's body is seen by everyone, its soul by no one. And the same is true of the soul of any other body, whether alive or dead, of living beings. There is, however, a strong suspicion that this class of object, which is wholly imperceptible to sense, [898e] has grown round all the senses of the body,2 and is an object of reason alone. Therefore by reason and rational thought let us grasp this fact about it,—
Clinias: What fact?
Athenian: If soul drives round the sun, we shall be tolerably sure to be right in saying that it does one of three things.
Clinias: What things?
Athenian: That either it exists everywhere inside of this apparent globular body and directs it, such as it is, just as the soul in us moves us about in all ways; or, having procured itself a body of fire or air (as some argue), it in the form of body pushes forcibly on the body from outside; [899a] or, thirdly, being itself void of body, but endowed with other surpassingly marvellous potencies, it conducts the body. — Ibid
It sounds like what we have sorted out as materialist or not in our modern lexicon is not a deal breaker to accepting the divine for Plato.