It looks like a "reap what you sow" situation. No one is looking good now.
I don't see this discussion as about whether a corporate PR team is allowed to issue a response. It's about the author childishly lashing out at an individual because he didn't agree with their decision.
Indeed, my belief is that this guy's and Uber's behavior are both not-ok, which is exactly why Uber doesn't get to complain.
No one looks good - he doesn't look good for how he behaved/communicationed, Uber doesn't look good for denying the payout on a valid report, and Hackerone doesn't look good for not enforcing a minimum payout on a valid report.