Other mistake: Near the beginning of the movie, the Dude is shopping at Ralph's. He is writing a check, and dates it September 11th, 1991. At the same time he looks up to see a TV with President Bush saying "This aggression (against Kuwait) will not stand." The incident against Kuwait started in the summer/fall of 1990, not 1991. The Stranger (Sam Elliot) and Walter also mention the Gulf War in the present tense.
Other mistake: As "Brother Seamus" slams the door of his Volkswagen shut before "fighting" The Dude, the volume of the radio drops, although he had the window rolled down and did not have time to roll it up before getting out of the car.
Chosen answer: There's no way of knowing. If the hiker was that far away, it could have been someone who happened to stray into the scene by accident. The filmmakers may or may not have noticed, but if they did, may have felt it added to the realism. I did this myself during the filming of a street scene for the TV show, "Northern Exposure." Filming was underway before I realised I was in the midst of it. I just kept walking like I was supposed to be there.
raywest ★