The rules changed in 2017. The person who told you this was possible must have purchsed their house before the rules changed. As of 2017, only Canadian citizens and PRs qualify.
To answer your second question, you would only have qualified for the rebate as protected persons if you purchased the property before November 14, 2016 and then became PRs within 18 months of this date. If you purchased your propertly after November 14, 2016 and were not PRs at the transaction closed, then you wouldn't qualify.
You can see these rules outline here:
https://www.ontario.ca/document/land-transfer-tax/land-transfer-tax-refunds-first-time-homebuyers#section-2