Earth got it’s noggin’ popped by a fairly large something or other just enough to change the cycle.
Could’ve been a couple of ‘somethings’ - plus the angle and location would not necessarily require it to be as big as something hitting closer to the equator.
It would not surprise me if a fairly hard knock had something to do with it. However, I don’t know where you got the idea that the asteroid that killed off the dinosaurs, did not also change the climate. Somewhere I have a book on climatology and earth’s history which, if I remember correctly, did describe changes. I will look for it and also Google now.
https://www.newscientist.com/article/2170015-asteroid-that-killed-the-dinosaurs-caused-massive-global-warming/ [This article addresses long term warming. Since it also referred to a theory that the Deccan traps killed off many dinosaurs before the meteor, I also found this Feb. 2019 National Geographic article covering detailed analysis of the Deccan by two university teams including the Alvarez family.]
https://www.nationalgeographic.com/science/2019/02/what-actually-killed-dinosaurs-volcanoes-heat-up-debate/
https://www.sciencedaily.com/releases/2017/10/171031111446.htm [This article says there is evidence of more severe immediate post event cooling. There are several other extinction article links here with controversial arguments about the decline of dinosaurs and severity of fires, etc.