Cleaner in world's 34th most expensive city, earns 6 times more than a cleaner in world's most expensive city, Singapore

I refer to the article “San Francisco janitor who earned S$380k in a year caught hiding in closet during work hours” (Straits Times, 8 Feb).
It states that “Mr Liang Zhao Zhang, who cleans the Powell Street station in downtown San Francisco, reportedly earned a total of US$271,243 (S$385,000) in 2015.
US janitor’s basic monthly salary S$6,856?
“The sum includes his basic salary of US$57,945 and an additional US$162,050 in overtime pay, public records released by non-profit organisation Transparent California showed.
According to Transparent California, there were at least 49 other janitors who earned over US$100,000 in 2015.”
His basic salary of US$57,945 works out to a monthly basic salary of US$4,829 (US$57,945 divided by 12) (S$6,856 (US$4,829 x 1.42)).
S’pore cleaner’s basic monthly salary S$1,160?
In this connection, according to the article “Fewer job vacancies, but more openings for PMETs” on the same day (8 Feb) in the Straits Times – the median gross monthly wage of a cleaner is only S$1,160 (920 vacancies).
According to the Ministry of Manpower’s (MOM) wages benchmarking tool – the median basic monthly wage of a cleaner is only S$1,050.
US cleaner’s pay is 6 times more?
So, does this mean that the basic monthly wage of a cleaner (janitor) in San Francisco may be about 6.5 times (S$6,856 divided by S$1,050) that of a cleaner in Singapore?
Similarly, does this mean that the gross monthly wage of a cleaner (janitor) in San Francisco may be about 10 times (US$100,000 divided by 12 months x 1.42 = S$11,833 divided by S$1,160) that of a cleaner in Singapore?
US cleaner’s pay is 3 times more than a management executive in S’pore?
By way of contrast – the median gross monthly wage of a management executive (1,210 vacancies) is S$3,409.
So, does it mean that a janitor in San Francisco may be paid about 3.5 times more (S$11,833 divided by S$3,409) than a management executive in Singapore?
S’pore: Most expensive city in the world – San Francisco ranked 34?
By the way, according to the Economist magazine – Singapore is the most expensive city in the world, whilst San Francisco is ranked at number 34!