很明显你朋友读的不仔细
If you are a student pass holder, you must have purchased the goods in the last four months before the expiry date of your student pass and remain outside of Singapore for a minimum period of 12 months after departing with your goods.
我的理解是不需要补税,1年期限只针对学生签证
Are you eligible for a GST refund? You must be a tourist and must meet the following criteria:
You are not a Singapore Citizen or Permanent Resident;
You spent 365 days or less in Singapore in the last 24 months before the date of purchase;
You have not been employed in Singapore in the past six months before the date of purchase;
You are not a crew member of the aircraft on which you are leaving Singapore by;
You are aged 16 and above at the time of purchase;
If you are a student pass holder, you must have purchased the goods in the last four months before the expiry date of your student pass and remain outside of Singapore for a minimum period of 12 months after departing with your goods.
You are leaving Singapore from Changi Airport or Seletar Airport. You will not be eligible for a GST refund if you are leaving by the Causeway.
You must have made your purchases within two months from when you apply for a refund.
https://www.visitsingapore.com/travel-guide-tips/tourist-information/gst-tax-refund/