Yeah, I don't think they're literally meaning "hurt" here.
Maybe a better analogy is where you're having a conversation with someone, and they throw in a double-negative. It's not like you're literally unable to work it out, but you need to engage with it consciously for a second. In a high-stakes conversation, that's just something that's good to avoid.
A memorable example of this for me (if a bit of a tangent) was when Felix Baumgartner was doing his mega parachute jump, and they kept screwing up the comms for which direction the wind was coming from / going in: https://youtu.be/rNhmYaWiPEk?t=4200
(by convention, people talk about wind in terms of the direction they come from).
I think the whole thing here is that driving involves a lot of modelling other drivers and their intentions, so our tolerance for bad UX that requires conscious thought should be really low.
I think the author is more accurately simulating how his brain will feel when he's flying down the road, tracking the trajectories of the very fast metal boxes surrounding him, and suddenly encounters a non-standard ambiguous signal. Turn signal decoding should be instant and unconscious, and this mini signal disrupts that. If anything I think he's understating the risks.
