It only voids the warranty if they can prove it caused the issue. They can try to claim otherwise, but it's actually illegal for them to do so.

I had Dell try to do this with a laptop with upgraded RAM that had a bad CPU. They said the upgraded RAM caused the issue and the warranty was voided, so I demanded to see the diagnostic logs that showed this (because I had diagnostic logs that showed it was a physical issue with the CPU).

They processed the warranty repair.

As an aside, that was the only time the BSOD was actually useful to me.