Why did Kyle Reese still tell this to the boy?

Question

In the end of Terminator: Genisys,

Kyle Reese tells his younger self that Genisys is Skynet.

Why would he do that if they think they

already won the battle against machines? Did they plan for some kind of time-machine loop?

Answer 1

Kyle Reese is the loop.

Reese remembers 2 timelines. The "original" with Judgement Day in 1997, and the altered timeline with Judgement Day in 2017. In his memories from the altered timeline, he remembers living in that house with his parents. He remembers his encounter with Sarah in the stairwell. And he remembers to repeat to himself that Genisys is Skynet because he told his younger self to remember it. Probably Sarah and Pops realized that they had to ensure that event took place otherwise when Reese came back, he wouldn't know what to do.