Intriguing case, so many things just do not make sense and seem illogical. IMO, If Mackenzie knew the person connected to the house being searched and intended to meet up with him/her, or spend the night there, she would have had the ride drop her there rather then minutes away in a park at the wee hours of the morning, there is just no sense as to why "that person" would have her go to the park and then pick her up if they were friends or already knew each other in any capacity and he/she lived only minutes away.
It has been mentioned by a few posters that the Lyft driver said she greeted the person picking her up in a manner that suggested they knew each other. I think that if the person picking her up was a "hook-up of any type" then Mackenzie would have been corresponding with him/her via social media for some time period and, imo, of course Mackenzie would greet him/her in a friendly or flirtatious way that suggested some familiarity, especially if it were to be/was a potential hookup or maybe there was a previous hook-up.
I am starting to wonder if perhaps "this person/perp" was maybe a previous hookup and maybe a spouse found out or someone was on to him/her (perp.) having a relationship with Mackenzie and the perp. maybe decided any evidence of Mackenzie had to "disappear". This case just seems like a cover up from the moment she was left at the park. IMO