Tests have shown that the eyes see the object (a bike) and the brain understands it saw something, but the "fight or flight" reflex, of sorts, is not triggered because the object (a bike) is not a threat to the safety of the driver, so the normal routine of pulling out from the stop sign is not interrupted. If you had been an 18-wheeler, they'd have probably not pulled out.

I'm glad you're attentive, and this again reiterates the need for ....

riding defensively.