Did you do a urine test, or was he looking at a blood panel and said that?
Regular MMJ users can test positive up to 100 days after last use with a urine test. Blood tests for THC levels are completely non standard, typically used only in cases of criminal investigations where impairment is suspected. The urine test does not detect THC but a metabolite it leaves behind, so the urine test cannot be used to determined impairment, only if you have had marijuana or not.
For a GI to purposefully request a THC blood test would be seen as a waste of taxpayer's money and the RAMQ would never allow it. Either he suspected you used, wanted to confirm it, bluffed about seeing results to get you to admit it, or he had you pee in a cup for that purpose.
Either way it's weird.