Why would it be somewhat surprising to see a guide dog without its owner?

Because guide dogs are assistance for blind or visually impaired people.

Explanation:

So, if a guide dog is alone it means that someone who has some visual problems needs helps asap. Therefor, it's a person in high risk. That's why is alarming to see a guide dog without its owner.

i pretty sure it is old

explanation:

ichabod crane is a fictional character and the protagonist in washington irving's short story, "the legend of sleepy hollow", first published in 1820. in popular culture, this story is sometimes retitled as "the headless horseman."