It turns out that the reason is that screening for basic math competency could be discrimination, because it reduces the chance of hiring for minorities who do less well at math testing. If the quiz were carried out in US, the company would need to prepare some report stating that math is essential to the job, which would be very cumbersome and costly to do scientifically.
I found it ridiculous as the position clearly needed math and I believe basic arithmatic is a valuable skill to ask for majority of the jobs, even for low-skill positions like cashier at Walmart. While eliminating discrimination is a great cause, all the band-aids to make the issue look less bad is shameful. Instead of improving basic education for minority communities (which costs some money now with high return from enhanced labor productivity and less welfare), our governments/society artificially discriminate in the opposite direction and suppress valid criteria that are statistically unfavorable to minorities.