Thank you for the feedback so far guys - much appreciated.
I have managed to find the METARs for the flight.
The cancelled flight was due to depart at 2030 (all pax were onboard sitting down at this time with doors closed):
METAR EPPO 162030Z VRB01KT 0500 R28/1500 FZFG NSC M06/M06 Q1035
It was still at the gate at 2100 having been delayed due to weather:
METAR EPPO 162100Z VRB02KT 0600 R28/1900 FZFG NSC M05/M06 Q1035
The pilots then cancelled the flight at 2330:
METAR EPPO 162330Z 24003KT 0300 R28/0650 FZFG NSC M03/M04 Q1034
The next morning, the rescheduled flight departed on time at 0630:
METAR EPPO 170630Z 20002KT 0400 R28/0700 FZFG VV001 M05/M05 Q1034
How can that be? The visibility, RVR and FZFG is just as bad for the rescheduled flight (if not, worse) than the cancelled flight?
I believe the challenge to this Hungarian LCC is not that the flight was cancelled due to "extraordinary" weather, but why was the following morning's flight able to depart in similar/worse wxr conditions?