He kill his father Kyle (David Denman) on what’s supposed to be a camping trip, but was secretly Kyle’s attempt at killing his son. Kyle tries to kill Brandon with a hunting rifle, but Brandon’s invulnerability sees him safe and sound. The son kills the father with his heat vision, and returns home just as his mother, Tori (Elizabeth Banks) accepts the fact that her adopted alien son is, in fact, evil.
Article source: https://www.cinemablend.com/news/2472263/brightburn-ending-what-happened-and-what-it-means