The technicians, it says, had "limited" experience in performing the check and that the magnastick readings were "likely not correct".
I can quite believe that. I worked for several airlines in the Middle East before I retired and a decision to fuel stick an aircraft was a big deal (with possible delay indications) simply because the Engineers and Technicians had no experience of the task. Many didnt understand the concept and were totally lost when it came to reading the charts - this was not because they were bad engineers or technicians it was just that those airlines tend to use new modern aircraft where the fuel systems are usually accurate and reliable, they just dont ever need to stick the tanks. I grew up on DC10's and other old birds were we did stick checks before each flight so a task that was easy for me to carry out on a 777 (say 15-20 minutes) could take 2 hours for inexperienced technicians.
When I say they didnt get the concept it appears that the SQ guys didnt either - you do a stick check when you dont trust the onboad fuel system and want to know exactly what fuel is onboard so checking all the tanks is obviously needed.