They can't because it's not true. The only way to find a third-party source to back that up is either use the one Swedish(?) study, which has been refuted by its original authors or some really ancient source with old data.

Depending on the way a country produces most of its electricity, EVs will outperform ICEs in emissions in just a few years. And that's mostly ignoring the emissions from drilling oil, refining it to petrol and moving said petrol to stations.