How does DSA provide non-repudiation in proving a document was properly displayed (not altered or displayed incorrectly)?
I'm trying to get my head around how the crypto solves this problem.


It doesn't. You need to trust the platform you use to do the signing.

For instance, my bank has replaced the "signature" generation device that I previously used with one that displays the actual transaction, so I don't have to trust the information on the computer screen that much.