Let me clear some things up as I have experience with places like VTT (but not VTT specifically) in my career.
VTT is a company that you pay to run tests for you. You bring them a product, tell them what tests you need done, and then they do them with honesty and expensive well calibrated gear. Frequently you also send engineers along with your product to provide on the spot support for the testing. It's very likely it was a Donut engineer who setup the cell, attached the heatsinks, adjusted the connections, etc. This is pretty standard, VTT just runs verified tests, they're not experts on your product. Then they give you an official honest report recapping the tests done and the results.
VTT is not an auditor for verifying claims, at least beyond the scope of the test you task them to do. They are a friendly business partner that you pay large amounts of money to for getting you verified tests done on your product.
I really cannot stress enough that VTT is not in it to disprove anything. It's incredibly suspect that in a battery capacity test, Donut did not have VTT verify cell weight or dimension. It's also important to understand that VTT would not request to do this either, because VTT just runs the tests you pay them to, as you tell them to do it. So if donut shows up with a different cell for each test, VTT would not skip a beat, because they are not auditing, they are just doing the tests they are paid to do.
Normally places like VTT thrive on compliance testing, where a regulation outlays the tests needed to be passed, and VTT provides the service of being the third party to run and sign off on those tests. Those tests are then submitted to the regulating body and they are the ones who pass/fail you, not VTT. They just do tests and collect money.
So Donut is writing their own "regulations" here, so they are just having VTT do whatever tests they want as they want them done.
The real test would be someone not affliated with donut taking one of these cells to VTT.