As far as I remember, I don’t think this is talking about the Exodus from Egypt. It’s mainly talking about the conquest of the land.
In any case, you can compare a few more cases of “did not know,” etc., where the meaning probably is as the Rabbi said:
Exodus:
(6) Joseph died, and all his brothers, and all that generation. (7) But the children of Israel were fruitful and swarmed and multiplied and became exceedingly, exceedingly mighty, and the land was filled with them. (8) Then a new king arose over Egypt who did not know Joseph.
Deuteronomy:
(10) And that whole generation also was gathered to its fathers, and another generation arose after them who did not know the Lord, nor yet the deed that He had done for Israel.
(1) And you shall love the Lord your God, and keep His charge, His statutes, His ordinances, and His commandments always. (2) And know this day: it is not your children who did not know and did not see the discipline of the Lord your God, His greatness, His mighty hand, and His outstretched arm, (3) and His signs and His deeds that He did in the midst of Egypt to Pharaoh king of Egypt and to all his land, (4) and what He did to the army of Egypt, to their horses and their chariots, when He made the waters of the Sea of Reeds flood over them as they pursued you, and the Lord destroyed them to this day, (5) and what He did for you in the wilderness until you came to this place, (6) and what He did to Dathan and Abiram, sons of Eliab son of Reuben, when the earth opened its mouth and swallowed them, their households, their tents, and every living thing at their feet in the midst of all Israel. (7) For your own eyes have seen all the great deed of the Lord that He did. (8) Therefore you shall keep all the commandment that I command you today, so that you may be strong and go in and possess the land that you are crossing over to possess, (9) and so that you may prolong your days on the land that the Lord swore to your fathers to give to them and to their offspring, a land flowing with milk and honey.
Judges:
(1) These are the nations that the Lord left, to test Israel by them—all those who had not known any of the wars of Canaan; (2) only in order that the generations of the children of Israel might know, to teach them war, at least those who had not known it before.
Samuel:
Now the sons of Eli were base men; they did not know the Lord.

The original passage in the Book of Judges says this:
{Open paragraph} 6 Joshua sent the people away, and the children of Israel went each man to his inheritance, to possess the land. 7 And the people served the Lord all the days of Joshua, and all the days of the elders who outlived Joshua, who had seen all the great deed of the Lord that He had done for Israel. 8 And Joshua son of Nun, the servant of the Lord, died at the age of one hundred and ten years. 9 And they buried him within the border of his inheritance, at Timnath-heres, in the hill country of Ephraim, north of Mount Gaash. 10 And that whole generation also was gathered to its fathers, and another generation arose after them who did not know the Lord, nor yet the deed that He had done for Israel. {Open paragraph}

From here it seems that there is a contrast between the generation of the fathers and the generation of the sons, in the sense that the generation of the fathers directly witnessed the deed of the Lord, whereas the generation of the sons only heard about it from their fathers but did not witness it themselves. Therefore the force of the impression made by the deed of the Lord was much less evident in their consciousness. That is also a natural process: a generation that itself witnessed something very unusual will be deeply affected by it, whereas in the next generation there will be a noticeable decline in the intensity of the impression left by that unusual event (like the Holocaust or the establishment of the State of Israel).