Thing with something like a bucket truck or boom lift is that they can basically act as a catapult. The harness would be attached with a lanyard somewhere on the boom or in the basket/bucket within operator reach. An accident can still involve injury, and possibly even death. But if you're wearing a harness and lanyard, it keeps ya from getting ejected, ejection being much less survivable.

Don't want to speak ill of the dead or speculate too much, but there were very likely multiple safety rules being broken. From PPE, maybe traffic control, maybe inexperience. Won't know until the investigation is done.