Traces? That's completely meaningless. THC is fat soluable. A person can have "traces" of THC in their system for months after ingestion.
I didn’t see any info on the actual levels. Also the article says “drugs” so it isn’t that clear.
I think the relevance is Martin didn’t want to get in more trouble while on suspension from school, and knew he coukdn’t pass a drug test. Also, pot symptoms can go from mellow to paranoid.