The story says "outdated" data but it's not clear what that could be in this context and why including older data would be bad? Something to do with not accurately capturing the current mix of variants, maybe?

So the issue is that they've included too much data leading to (in the DSMB view) inaccurate efficacy rather than incomplete data.

Nonetheless this is a management failure on their part because any disagreement with the DSMB over which data to include should have taken place privately before publication of the results. For all I know they have good reason for including this older data but it's not a good look to have your DSMB disagree with you in public now.