So does the text imply that Noah, and mankind, were vegetarians before Gen 9:3 (“every moving thing that liveth shall be meat for you”)?

I have already discussed this question above, but let us re-examine it briefly in light of this passage. I think it is tolerably clear from what we said earlier that, probably, men were not just vegetarians. The Cainites were surely not above eating meat. But in that case, why say the animals “shall be meat for you; even as the green herb have I given you all things”? That is a fair question. After all, the text seems to be an allusion to this: “Behold, I have given you every herb bearing seed, which is upon the face of all the earth, and every tree, in the which is the fruit of a tree yielding seed; to you it shall be for meat.” (Gen 1:29) Perhaps it also refers to “in sorrow shalt thou eat of [the ground] all the days of thy life” (Gen 3:17), which God told to Adam; there, too, there is no reference to animal meat. Could it be that God did not approve of meat eating, even though he tolerated it, but that here, now he officially sanctioned it on grounds that man would certainly continue in his practice, just as he would continue to have multiple wives? That would imply that God’s laws become laxer in order to accommodate was once regarded as sin; and that sounds unlikely. I think it is fair to say that God always did approve of meat eating, and the reason he says man may eat meat now, whereas he did not before, is that in the times before the Fall, man did not eat meat because he did not have to. Now, essentially, the difficulty of life in a fallen world has made meat-eating a practical necessity. God specifically blesses meat-eating because man is beginning a renewed life in this fallen world, in which meat-eating is necessary.