Starship has only launched four times this year (January 16, March 6, May 27, and August 26) at around 23:00 UTC (5pm CST/6pm CDT) each time.

It is likely that you saw other rockets (Falcon 9 being the most frequently launched). The "slow-forming starburst" is most likely from the exhaust plume in vacuum; once the rocket is high enough to no longer be in earth's shadow the plume catches sunlight and becomes very visible on the ground to an observer in darkness. See https://en.wikipedia.org/wiki/Space_jellyfish