Honestly could you blame him for not liking Java in 2007? Between the many layers of abstractions the frameworks used, the exceptions and the sluggishness to compile it was not a compelling stack
Java's problem never was the language which has been as serviceable as any other since the JDK1.4 days. It is straightforward to compile (no metaprogramming, type erased generics), linking is delayed to runtime and dependencies are all precompiled to bytecode which _should_ make for very fast builds.
The problems came from the multitude of Internet-bubble era tool vendors which overcomplicated everything in order to sell high priced "corporate-level" solutions and imposed that certain coding style. Java is still known for this today because it appears in so many vintage codebases and is still being applied by coders who never revised their practices from 22 years ago.
My theory is that Rob Pike was jealous of Java because it has succeeded with a model similar to his own Inferno (bytecode, C syntax) and this aligned with Google's ask of developing something that would be outside of Sun's lawyers reach.
While it's been made to work, the JVM itself isn't the greatest VM for hosting other non-Java-shaped languages because of this.