It's not at all inconceivable someone is operating stealth aircraft in that region. Reagan was willing to share[1] with Britain stealth in '86, so perhaps 30 years later, it's easier to obtain and someone sold some to Chile or its neighbors. The US, Russia, and China all have it.

1. https://theaviationist.com/2017/01/02/in-1986-u-s-president-...