Just a question I have regarding drugs and police officers just letting them go????

So someone very close to me dozed off at her job last night & of course they blamed it on drugs. This person DOES have a history with drugs, but apparently is sober now, I don’t really know. She had a meth charge in like 2018… This man at her work called the cops on her last night, cop interrogated her in the parking lot.. Cop eventually searched her car & her purse, said they found all kind of residue on her belongings and even did drug tests on all the residue he collected right there in the parking lot, said it came back positive for meth… but then… he said “I’m just gonna let you go on and leave, but I’m not letting you drive so call someone to come get you” (she called me).. and idk, I’m just wondering if he really found all this residue that came back positive, would he really have just let her go?! Or was he just sayin that it was positive for meth to scare her…
He kept her there for about 2 hours interrogating her, he was apparently off duty, wasn’t in uniform, but had a trainee with him. He kept saying she was gonna go to jail bc of all this residue that came back positive, but eventually just let her go??