I'm making a best effort guess based on the evidence to understand how the company works but yes, you can't prove one way or another. All I can really say is
Valve's website doesn't average any position related to PR, marketing or community relations
I've never seen a marketing position advertised on glassdoor for Valve
Valve's public-facing communication is legendarily poor, almost entirely buried in patch notes
So I'm just putting 2 and 2 together here. If Valve actually has a community relations team, please God let me work there because that must be the easiest job on Earth.