They are purchasing using hard cash (ie USD) outside Lebanon and then transferred there. The article is a bit confusing but this is the key bit:
An agent in Nigeria will collate these sums, buy USDT, and send it to one of the top-level suppliers in Lebanon. Once they have sold it on, they will disburse cash to the originally intended recipient of the remittance.
It's a way to transfer USD (value) to your family in Lebanon. The dealer in Lebanon gets Tether (from the agent in Nigera), and gives cash USD to the family in Lebanon, minus their commission.
The Lebanese pound is never used.