Actually that makes perfect sense. In normal times, Dollar/Thrifty is supposed to be the cheaper, crappier, less rewarding, alternative. That usually means retired Hertz cars, aging with high mileage.
But Hertz is now dealing with the challenges of holding inventory and offering a differentiated customer experience. It sounds like the 2018 was one of the lease returns Hertz recently bought, to deal with the new car shortage. It would be on-brand to offer it to a discount channel, rather than through the premium counterpart, whenever possible.