I needed more context, so I looked up the story.
A child was standing on a street-corner. He leaned with one shoulder against a high board-fence and swayed the other to and fro, the while kicking carelessly at the gravel.
Sunshine beat upon the cobbles, and a lazy summer wind raised yellow dust which trailed in clouds down the avenue. Clattering trucks moved with indistinctness through it. The child stood dreamily gazing.
After a time, a little dark-brown dog came trotting with an intent air down the sidewalk. A short rope was dragging from his neck. Occasionally he trod upon the end of it and stumbled.
"Moved with indistinctness"
This is kind of an abstract description. Based on the rest of the paragraph, the writer wants you to imagine a hot and dusty summer day. The trucks are driving noisily down the street, but the boy isn't really paying attention to them, because they are just part of the background.