Are you saying that they are essentially giving you $29000 for your truck? If so, then I think you have it right. They probably cut the bank a check and you a check. Or they just cut you a check that you take to the bank, either way, same deal.
Buying, if you can afford it, is always better than leasing imo. I leased for a couple of reasons, not just that, but at the end of the lease you will be either buying the truck probably for more than you want to pay, or turning it in and going through the whole money down/etc negotiations all over again. plus you have to deal with mileage. If it isn't that I've never seen anyone get the "advertised" lease price (its almost always more for some reason), its that they get you with the 10000 miles a year lease which seems the typical starting point nowadays.
So its $149/month but what you don't know is that is base model, 10000 miles a year, and $3000 down. By the time your done figuring it all out, your payment is closer to $300/month, and you don't own any of it.
If it were me, and I liked the truck and it had low mileage like you said, and no issues, I would probably just keep it. Refinance it, or whatever. At least you know the history of your truck. Or if you want a new one, buy it if you can. The way the prices are nowadays, I'd almost look for a used 2018 or wait a bit to find a used 2019 and buy that. Saves you some money, and still practically a new truck.