Is a pilot responsible for CTAF announcements in this scenario? A Cessna 525 Citation Jet is coming in to land and a single-engine Cessna 150 is taking off at a small airport with no ATC. The Cessna 150 stays in continued radio contact and the Cessna 525 Citation Jet does not.

An accident occurs where the Cessna 150 clips the Cessna 525 Citation Jet on the tail end. The Cessna 150 crashes and burns. The people in the Cessna 150 pass away and no one is injured on Cessna 525 Citation Jet. 

Is this labeled as an accident although the Cessna 525 Citation Jet did not stay in radio contact after landing when the Cessna 150 attempted to take off?

https://www.cbsnews.com/news/marion-indiana-airport-planes-collide-2018-04-02/
In the U.S., the definition of an accident is covered under 49 CFR Part 830.2:  (emphasis is mine)

§ 830.2 Definitions.
As used in this part the following words or phrases are defined as follows:
Aircraft accident means an occurrence associated with the operation of an aircraft which takes place between the time any person boards the aircraft with the intention of flight and all such persons have disembarked, and in which any person suffers death or serious injury, or in which the aircraft receives substantial damage. For purposes of this part, the definition of “aircraft accident” includes “unmanned aircraft accident,” as defined herein.

From your question, this appears to clearly be an &quot;Accident.&quot;