I don’t think the driver needs an excuse; nothing he was doing was illegal and accidents do happen. That said, the article says,

“Autopilot” as it occurs in planes empowers the pilot to be able to leave his seat. This is the problem with calling cruise control “autopilot” and using words like “autonomous” to describe the system’s functionality.

If it’s just glorified cruise control the words “autopilot” and “autonomous” should not be used for extraordinarily obvious reasons.

It would’ve been both. The article clearly states neither he nor the system’s sensor array saw what the truck driver was doing.