His opinion is that the EU wasn't strict enough to prevent manufacturers from cheating on emissions tests for diesel cars

The EU incentivised deisel a lot more than other regions under the misguided assumption that deisel would reduce CO2 emissions and that NOX emissions would be easy to reduce in future, but in actuality they ended up being about the same as regular petrol cars once NOX emissions were actually reduced.

They had a big incentive from oil refineries in the EU to use diesel after the oil crisis as diesel is always produced during oil refinement, and from car manufacturers to be able to keep selling diesel cars. Because of this they continued using outdated emissions tests for diesels cars for decades.