In regards to the spy conversation, I agree with others that it should probably be Wendy. However, I always found Mackey's behavior extremely off. Upon the first time you meet him, he's bullshitting you under the guise of being a "bro." Which he later admits to. But why admit to that? Then he proposes a deal where he tells the MC that he's rich and can help out the MC for staying off his back, but then makes up a poor excuse for why he's rich when he says " I dunno...gravel or some shit." And yes, he might just have no connection to his family or be dumb.
However after these first interactions with him, he's notably more involved in basketball, (i.e. agreeing to the early morning practice, and another occasion where somebody said that they were surprised Mackie was coming along.) as noted by Harper a couple times. This goes directly against what MC was told was his usual behavior, which was just coasting through school and basketball. Why all of a sudden the interest in basketball and being involved with the MC?
As far as somebody being a spy for Ryker but not of his own word...I'm not sure. One could argue that his helping the other players at the bowling alley plays into this. If he was working for Ryker directly, he would have sucker punched the MC or just fucked off somewhere while everything was going down.
As a side note, given how we're told he likes making EDM/synthwave/whatever, that also tells us he does at least know his way around tech quite a bit, so he could possibly be using cameras.
As an additional side note, I find it weird that Ayden and Skye were the only ones from the team to join the fight outside. Yes there's the whole "oh yeah the other players had to pin down Damien and another staff member", but I dunno, that element of the story always rubbed me the wrong way.
Feel free to call me straight up wrong, I'm just spitballing here and he's a character that's always seemed off to me.