It is a busy location but there is no charge to park elsewhere at Trentham Gardens, which has a a lot of car parking area.
It is a new supercharger facility with the latest CCS charging plugs, which I've just established the likes of Hyundai, Kia, BMW, Audi, Mercedes, MG, Jaguar, Mini, Peugeot, Vauxhall / Opel, Citroen, Nissan, and VW and maybe others by now have all adopted. Perhaps like you suggested they assumed they would get a charge but didn't and just used the bays for a convenient park.
I think other Tesla drivers will be getting very annoyed when other OEM's are preventing access to Tesla vehicles, which already seems to be happening, even if they don't get functioning connectivity.
Tesla's dedicated charging network was a big incentive to purchase a Tesla in the first place, when that gets shared between other OEM's the incentive will disappear.
In my opinion other manufacturers should only be given access to the Tesla network, after they have installed an equal amount to the charging infrastructure that Tesla has. It may offer an additional revenue stream to Tesla but the annoyance to Tesla drivers I feel will outweigh the benefits if queuing to charge becomes an issue here, as it is is in areas of the USA.
The honeymoon period seems to be coming to an end for the early Tesla adopters!