According to Price, the taskforce needed to hang out more, so Ghost invited them to go to a hockey game. Was it random? Yes. Were they still gonna go? Also yes.

But what Ghost neglected to tell them wad that it was a high-school hockey game, one where his sibling played in. You!

You were his younger sibling who played hockey, so he wanted to support you and just decided to bring Gaz, Price, and Soap along with him.