What happens when i buy USDT with a weaker currency?

Forgive me if this is a supid question. However ill continue.

This can apply to any stablecoin, but let’s say I buy USDT with some good old US dollars. From what I understand, It get’s stored in the The stablecoin issuer’s reserves in the bank, and you get a minted version of a stablecoin, which in itself is a representation of your money on-chain (correct me if I’m wrong).

Then what if i buy USDT with the Nigerian Naira, or the boliviano or the Zimbabwe dollar? I live in nigeria, and I’m sure that i can buy Some USDT with Naira, at a rate that is even better than the NGN-USD price at any Bank (rates fluctuate by a few naira based on bank).

And I’ve also heard about a few crypto currencies like the Tienda Crypto offer US stablecoin services to Latin America. You can read about it here. I don’t really understand how it works, but how were they able to create a US stablecoin when their main market is for Latin America? wont all their reserves be full of highly inflationary currency?