Kyle has killed the Chucky head that Andy was keeping locked in his house.
Prior to having his throat cut by Tiffany, the car salesman praised the car by stating "a true classic never goes out of style." As longtime Chucky fans will no doubt remember, that was also a famous line offered by the killer doll in Bride of Chucky (1998). In his case though, Chucky was referring to the endless joy of murdering somebody with a knife.
While trying to slip up Nica in her ruse, Tiffany questioned her about Niagara. This was where Tiffany and Chucky reaffirmed their twisted love during 1998's Bride of Chucky. The moment came immediately after Tiffany had creatively killed another honeymooning couple, and led to the conception of Glen/Glenda from Seed of Chucky. As such, Tiffany wasn't lying when she recalled the location as being central to many fond memories.
The car in the flashback that Chucky and Tiffany buy, is notably similar to the demonic Christine from the Stephen King book and subsequent John Carpenter movie of the same name right down to having a deadly legacy.
Andy recounted to Kyle some of the lessons he'd learned at military school. As well as shedding light on his understandably broken psyche, this implied Andy might have still graduated despite the traumatic events.