So much for journalism, I guess. The only estimation that's happening is of the remaining battery range. The odometer is recorded exactly. The case's whole evidence is some random anecdotes of people who feel like their odometer is higher than they expect.
No it couldn't be, don't be silly. Dieselgate was a systemic industry-wide problem, with most manufacturers involved to at least some extent, and not just car makers but also the supply chain (for whatever reason, in the popular imagining it was mostly just VW, but in reality the corruption was far more widespread). Even if the allegations are correct, this is, at worst, just a single manufacturer; no reason to think that it's more widespread.