The complainant also raised concerns that the driver may be a private-hire vehicle driver.
The 137-year-old Japanese law prohibits any person from challenging another to a duel.
Her grandson is now in remission and undergoing follow-up treatments.
A netizen claimed the customer was the first to verbally abuse the staff member.
The office worker had relied on the sugary drinks to cope with work stress.
Police are still working to determine the motives behind the man's erratic actions.
Netizens showed support, suggesting that the WP's outreach posts indicated internal unity.
The owner added that the car was serviced regularly and had not undergone any major repairs.
The incident drew mostly critical reactions online, with netizens questioning the decision to involve the police.
A 41-year-old motorcyclist was taken conscious to Tan Tock Seng Hospital.