Yirmiyahu paraphrases Bamidbar

Last Shabbat I was skimming Yirmiyahu because I was looking for a particular verse and in that moment wasn't near a concordance (what would we Tanach-loving, Shabbat-observers ever do without a concordance???), and I came across something that frankly shocked me. I had studied Yirmiyahu before and I've written on that in the blog. But I was struck by the following verses (48:45-46):

"בְּצֵל חֶשְׁבּוֹן עָמְדוּ מִכֹּחַ נָסִים כִּי אֵשׁ יָצָא מֵחֶשְׁבּוֹן וְלֶהָבָה מִבֵּין סִיחוֹן וַתֹּאכַל פְּאַת מוֹאָב וְקָדְקֹד בְּנֵי שָׁאוֹן. אוֹי לְךָ מוֹאָב אָבַד עַם כְּמוֹשׁ כִּי לֻקְּחוּ בָנֶיךָ בַּשֶּׁבִי וּבְנֹתֶיךָ בַּשִּׁבְיָה."

"In the shelter of Heshbon fugitives halt exhausted; for fire went forth from Heshbon, flame from the midst of Sihon, consuming the brow of Moab, the pate of the people of Shaon. Woe to you, O Moab! The people of Chemosh are undone, for your sons are carried off into captivity, your daughters into exile."

What's surprising about this is that this a paraphrase from one of the most intriguing chapters in the Book of Bamidbar (Numbers), chapter 21, which includes a phrase from something called "The Book of the Wars of the LORD" (ספר מלחמות ה'), and - more relevant here - a quote from nameless "bards" (מושלים) (21:28-29):

"כִּי אֵשׁ יָצְאָה מֵחֶשְׁבּוֹן לֶהָבָה מִקִּרְיַת סִיחֹן אָכְלָה עָר מוֹאָב בַּעֲלֵי בָּמוֹת אַרְנֹן. אוֹי לְךָ מוֹאָב אָבַדְתָּ עַם כְּמוֹשׁ נָתַן בָּנָיו פְּלֵיטִם וּבְנֹתָיו בַּשְּׁבִית לְמֶלֶךְ אֱמֹרִי סִיחוֹן."

"For fire went forth from Heshbon, flame from Sihon’s city, consuming Ar of Moab, the lords of Bamoth by the Arnon. Woe to you, O Moab! You are undone, O people of Chemosh! His sons are rendered fugitive and his daughters captive by an Amorite king, Sihon."

From the Hebrew in particular it's very clear that Yirmiyah was paraphrasing Bamidbar. Some of the phrases are exactly or almost exactly the same, and the general scheme and idea are the same: The fall of Moav, of the city of Sichon, via fire and flame. Yirmiyah stated these verses during his prophecy on Moav's endgame, part of a series of prophecies on the coming destinies of various nations neighboring Eretz Yisrael. Yirmiyahu clearly intended to draw a connection between his prophecy on the future of Moav and the apparent prophecy (again, who these bards are and what was their authority is unclear) brought in Bamidbar. Interestingly, the next verse in each passage has a different meaning entirely: In Bamidbar there's a further statement on the fall of Moav, while in Yirmiyahu there's a statement of hope - in the future Moav will be redeemed.