Did the impact event that caused the Chicxulub-Crater definitively and single-handedly cause the Cretaceous-Paleogene extinction?
No, it did not definitively single-handedly cause the KT mass extinction event. Around the same time, the Deccan Traps Large Igneous Province (India) was being emplaced. Flood volcanism has been associated with other mass extinctions, due to the impact on climate, sunlight at the surface, etc, of the output of huge volumes of sulphur-based gases.

The Chicxulub impact probably didn't hurt the extinction, but the large particulate material it distributed in the atmosphere would have sedimented out again entirely within a handful of years. Meanwhile, the Deccan Traps contain sediment layers intercalated between lava flows, some of which contain fossilised dinosaur eggs.

The reasons for mass extinctions (and whether they actually occur at all, as distinct identifiable events) remain poorly understood, but we're pretty sure the meteorite impact wasn't the only thing that did for the dinosaurs.