First, let me emphasize something that DoninGA said. We are assuming that the car was only for personal use, and there was no business use. If that assumption is not correct, just ignore everything that's been said here and start over with more information about how the car was used.
You might need a lawyer to sort this out. It's not clear what really happened. But here are my thoughts. (And I am not a lawyer.)
I assume that the lease gave you the option to buy the car at the end of the lease for $22,000. The third party was not a party to the lease, so he had no particular claim to the car, and the leasing company had no particular obligation to allow him to buy the car.
IF it's true that you never took title to the car, then you must not have exercised your option to buy the car. You returned the car to the leasing company at the end of the lease, and they sold it to the third party. (If you did exercise the option to buy the car, then you did own it, even if only for a few minutes, and even if your ownership was not registered with the DMV.) If you never owned the car, then you never sold anything, so you do not have any kind of capital gain. But somehow you ended up with $8,000. So the question is, what is the nature of that $8,000 that you acquired?
There are two questions that you have not given the answers to.
1. Did the lease have a provision giving you some kind of refund or rebate if the leasing company sold the car for more than the residual value that was estimated when the lease was signed?
2. You said that the third party paid the leasing company directly, but you didn't say how much he paid them. Did the third party pay $30,000 to the leasing company, and the leasing company then paid you $8,000? Or did the third party pay $22,000 to the leasing company and $8,000 to you?
If the third party paid $30,000 to the leasing company, and the leasing company then paid you $8,000, then the $8,000 might indeed be considered a refund of part of your lease payments, which, as DoninGA said, would not be taxable income. If the payment of the $8,000 was required by a provision in the lease, that would add strength to this argument.
But if the third party paid the $8,000 directly to you, then it would appear to be payment for some sort of service that you provided in facilitating his purchase of the car. In that case, it would be ordinary income to you, and it would be fully taxable. Again, it's ordinary income, not capital gain, because you didn't sell any asset.
I suggest that you consult a good tax lawyer.
