Funnily enough, just read this on the BBC app. It appears Derby postponed their match due to unsafe stands at the advice of police and the Safety Advisory Group (whatever that is)
The league are looking into it as it's been flagged up by Cardiff as "convenient" for Derby as they had quite a few injuries
No mention of referee involvement.
Derby v Cardiff: EFL request 'observations' from clubs after postponement - http://www.bbc.co.uk/sport/football/43464818