Another interpretation: "And it was turned." They said: because of them the good was coming upon us. Rabbi Yose the Galilean says, a parable: to what is the matter like? To one who had a field of a kor's measure fall to him as an inheritance, and so on. So it was done to Egypt: they sent them away and did not know what they sent away, as it is written, "And they said, what is this we have done?"
Egypt Sent Israel Away Not Knowing What They Lost
Yalkut Shimoni on Torah 230:14
דָּבָר אַחֵר, וַיֵּהָפֵךְ. אָמְרוּ, בִּשְׁבִילָם הָיְתָה טוֹבָה בָּאָה עָלֵינוּ. רַבִּי יוֹסֵי הַגְּלִילִי, אוֹמֵר מָשָׁל לְמָה הַדָּבָר דּוֹמֶה, לְאֶחָד שֶׁנָּפְלָה לוֹ בֵּית כּוּר בִּירֻשָּׁה וְכוּ', כָּךְ נַעֲשָׂה לְמִצְרַיִם, שָׁלְחוּ וְלֹא יָדְעוּ מָה שָׁלְחוּ, דִּכְתִיב, וַיֹּאמְרוּ מַה זֹּאת עָשִׂינוּ.