Delusional. I suspect they won't even hit 1.8 million genuine tourists.
The few tens of thousands that have arrived since Nov 1 are not typical tourists. They are mostly those with a more long term connection to the country and have been waiting on entry requirements relaxing so they could make the journey.
Genuine tourists won't waste their time. They want a relaxing holiday and there is nothing relaxing about entering Thailand currently.
18 million tourists next year? That's a good one...