It is a pity you hadn't discovered this forum before you made any appeal. (Not so) Smart Parking are one of the easiest to defeat at the initial appeal stage because they do not issue Parking Charge Notices (PCNs) that comply with PoFA. What this means that as long as the Keeper appeals without identifying the driver, they have nowhere to go.
By appealing as the Keeper and blabbing the drivers identity, inadvertently or otherwise, with silly statements such as "I did this or that" instead of just referring to the driver in the third person such as "The driver did this or that", the Keeper has thrown away the easiest of appeals that would have left (not so) Smart Parking in a Catch-22 dilemma.
Why? Because the unknown driver is always liable. The known Keeper is not under any legal obligation to identify the unknown driver to an unregulated private parking company. So, if (not so) Smart Parking do not know the identity of the unknown driver and because they do not rely on PoFA to be able to hold the known Keeper liable, they are stuffed.
If the Keeper has blabbed that they were also the driver when there was no legal obligation to do so, they have, proverbially, shot themselves in both feet! The Keeper and the driver are two separate legal entities.
The POPLA decision is not binding on you. However, are you willing to fight this as far as it is likely to go? You are going to have to weather a storm of useless debt collector letters. You can safely ignore any Debt Recovery Agent (DRA) letters such as those from DRP+. They are not a party to the contract allegedly breached by the driver. Never, ever, ever, communicate with a useless DRA. All they can do is try and get the low-hanging fruit on the gullible tree to pay up out of ignorance and fear.
What the most likely outcome will be a county court claim for the alleged debt which is easily defended. In the vast majority of cases, as long as the claim is defended, they will eventually discontinue. In the rest, the claim is struck out due to errors made by the claimants solicitor. Of the tiny number that actually go as far as a hearing, most are won.
So, are you prepared to fight this with the advice you will get from here?