No, it is assuming we have 50% of passengers during the night and 50% during the day – but the day and the night have different duration, therefore you have different # of passengers per hour of day vs per hour of night:
Day: 8,400,000/365/18hours = 1,278 passengers per hour
Night: 8,400,000/365/6hours = 3,835 passengers per hour
That in turn means that you have different utilisation rate for day and night:
Day: 1,278 passengers per hour divided by 2.100 taxis per hour = ~61% utilization rate (hourly supply of taxis exceeds hourly demand of passengers)
Night: 3,835 passengers per hour divided by 2.100 taxis per hour = ~183% utilization rate (hourly demand of passengers exceeds hourly supply of taxis)
I hope this is helpful! Please don't forget to upvote and if you have further questions, just DM me.