MOO and my speculation only but we may be looking at a friend-of-a-friend here.
I don’t believe ML was heavily into drugs per se. But she was coming back to exams after a stressful week and may have been looking for a “study aid” of some sort. It’s very common. If so, she may have texted a friend from the airport who said, I know someone who can help you out.
She could have contacted him, he gave her the park address for the meetup, and said he’d give her a lift home. And maybe she accepted the sketchy arrangement because they had a mutual friend.
100% speculation and 100% MOO.
ETA — another relevant quote...