It seems to me that someone should have noticed a 30 knot difference. After all, that's 20 percent of the correct number. Had they never flown that type of aircraft before that day?
In the SIA event a take-off weight transcription error, which remained undetected, led to the miscalculation of the take-off data, which in turn resulted in a low thrust setting and excessively slow take-off reference speeds. The system defences did not ensure the errors were detected, and the aeroplane flight management system itself did not provide a final defence against mismatched information being programmed into it.
CX changed their ACARS RTOW input page after several reports of entering ZFW instead of TOW into the available field. I believe one A330 even got airborne, however the difference in ZFW and TOW was less than 20T and the resulting RTOW had the same max flex temp for both weights.
Because the FMS performance entry used ZFW crew became accustomed to using the ZFW figure when using the "box".
Also blasting around in light weight A330s all day and occasionally flying A340s and even less flying on A346s meant a typical A330 TOW was often similar to a 340 ZFW.
The ACARS RTOW now requires crew to enter both ZFW and TOW, the RTOW does a cross check, if the figures aren't reasonable you get a check data message.
Simply human factors, rubbish in the box you get rubbish out, you need well written SOPs to prevent the swiss cheese event.