Están vs. Son
 

Discussing recent accidents in my neighborhood with my neighbor, I said, “Muchos de estos accidentes están causados por conductores desatentos.” My neighbor added, “Y son causados por personas que envían mensajes de texto.”

I’m pretty sure I heard him say “son causados.” So if that is what I heard, I’m now unsure which is correct and why.

Could someone please shed light on whether to use “están” or ”son” and why?

The passive voice is what you were thinking in English.
This is used in Spanish, but much less frequently than we use it in English.

Your neighbor corrected estar to ser because the latter is used to form the passive voice in Spanish.

Formula for the Passive Voice:
conjugated form of ser + past participle + por + agent

Thank you for responding, Rusty, and thank you for the link. That clears it up.