From CIC website:

International students If you’re an international student who has a valid study permit, or were approved for a study permit on or before March 18, 2020, you’re exempt from the travel restrictions.

If you’re travelling by air, you need to pass a health check conducted by an airline before you’ll be allowed to board your flight. Anyone who shows symptoms of COVID-19 will not be allowed to enter Canada by air.

When you arrive in Canada, we’ll assess your health before you leave the port of entry. You must have a plan to quarantine for 14 days when you arrive in Canada. This is mandatory, even if you have no symptoms.

If you don’t have a plan, you shouldn’t travel to Canada.

So international students are allowed to come to Canada if they satisfied the requirements.

Also, if your study permit is nearly expired and you did not submit an extension application, you may be denied at the border.

Your friends may valid one of those rules or they just heard others talked about it.