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.
I guess the agent probably has to buy bitcoin and exit if on some dollar offramp to get actual USD to give the family.
The problem is that now it just extremely risky
Most of the upper class has the USD denominated savings effectively kidnapped by their bank institution. Those funds are frozen or very highly capped (only say $200 $USD draw per week). No one can take them out in large chunks. It is extremely difficult to make payroll for staff (many companies paid payroll in USD instead of lira before the crisis).
You can use USD deposits to buy assets or cancel debt though. As long as the receiver / beneficiary of your money another lebanese bank. So, you can pay your debts, or transfer your money to someone else in lebanon. But you can't take physical dollars out for the same purpose.
There is also the concept of "fresh money" by which the bank will let you take out any money that you have recently received from abroad. That's what is making everyday living bearable for a lot of lebanese
This article doesn't go into where that comes from, but it's not unusual for criminal gangs to launder money this way. The agent themselves might not be a criminal, but they take often use the cash supplies from one and transfer back the value somewhere else (via a legitimate business) less a commission.
Whether they should have censored transactions in that instance is irrelevant. The fact remains that the coin does not belong to it's holders.
You must have missed that 1. Lebanon is very corrupt and 2. there is an official exchange rate. Someone is making a killing selling on the black market and buying with the official rate.
Its about 18,000 to 1 USD, at the moment.
It was 1,500 back in Sept 2019, and as the article states, it was at this rate since the 70s.
Source: https://lirarate.org/
Obviously, he'll need to run a full circle (back from Lebanese pound to USD) to refuel his reserves. In some countries where I have seen this, this is usually done through companies which have some license to buy USD at the government exchange rate to import stuff. Stuff is imported from offshore companies run by these same guys who will sell this product at some crazy markup (usually 100%) and then this profit is dumped through guys like in the article. Rinse and repeat.