breath-first doesn't mean it's not looking into subdirectories. It is, but it looks into each subdirectory before decending into the different subdirectories subdirectories.

So it enger first subdir, looks at files there, then goes back up, enters second subdirectory, looks at files there, ... After checking each subdir it goes into the first subdir oft the first subdir, looks at files there, then goes to second subdir of first subdir