Agree with that.
If source is PME then it needs to be TT if it's mounted outside a building. This is also dependent on your own risk assessment providing evidence there are no simultaneously accessible extraneous parts belonging to the PME system.
There is currently a "get-out" which allows use of PME "if not reasonably practicable". I suspect that is being used more than sensible by many EV charger installers. This also relies on a credible risk assessment (your neck being on the line in the court) to say that's all OK for whatever reasons you choose. The latter get-out will disappear completely in 18th as I believe.
And don't forget that the TT earth you provide needs to be LOW. Chargers (certainly 32A ones) will monitor EFLI and not allow charge if it's too high. Notionally 200 ohms, but don't believe it. I have it on good authority from a Renault tech that their chargers might need as low as 70 Ohms to operate reliably. - That is likely to need more than a 4' twig in the soil.
And don't forget type A RCD and probably a D type breaker.
I think you need to do some reading too