Having thought about it you're correct. Even if you over inflate your tyres it won't provide enough buoyancy even for the smallest Euro-car.

An alternative reading to it 'being idiotic' is that it was clearly an exaggeration to prompt some critical thinking about the original claim.

What critical thinking? The train from London to Paris is barely above 2 hours. Why on earth would you drive if you’re in hurry?

I was replying to "It is a six hour drive from Heathrow to Paris"

Well yes, but I’m just curious in what way was the original comment supposed to promote critical thinking

There's a train between the UK and France. It carries cars.

That I use regularly to actually drive from no-too-far from LHR to Paris and back. It's a thing I actually do.

And I can tell you, it might be theoretically in Google Maps land to do the journey in 6 hours, but IRL in this scenario it won't happen. Actual empirical evidence.