I'd assume they just haven't been unblinded yet.

They were all unblinded weeks ago, the authors are listed on the workshop website: https://beyondbackprop.github.io/

So, at this point, the most likely explanation seems to be that TFA was written prior to the unblinding, and then wasn't subsequently reviewed or updated before publication.

Hmm. Shouldn't papers all be unblinded at once when acceptances/rejections are sent out?

These are workshop submissions (which typically implies a more lightweight review process, for more exploratory work), and it is possible the same submissions are currently in blind review for other conferences in their final form.