He is a known shill who was actually paid by Oracle for a while. And disclosed it only after it was uncovered independently. Not exactly what I would call neither an impartial source nor a copyright law expert (he is a software developer and activist, no a lawyer).

Back in 2012, Florian Mueller (the blogger in question) was recognized as a consultant for Oracle in a lower court case that's been leading up to this moment (1).

(1) https://www.theverge.com/2012/8/17/3250148/oracle-tells-cour...

Even the pro-Google reporters I followed during the arguments yesterday concluded this appeared to be the lean. Both sides claim a ruling for the other side will be catastrophic to the software industry (both are wrong on this, mind you). But the questions seemed largely skeptical of Google's arguments, and one of the most notable claims the Google lawyer made was purely preposterous as a matter of law: That it would've been a lot more expensive to develop their own API and so they shouldn't have had to.

Reporters on Google's side of things seemed to think Goldstein blew conveying their side.