Why Koltlin imports all classes from the local package?

I have a Kotlin project with this structure:

.
└── org
 └── gradle
 └── sample
 ├── JoinUtils.kt
 ├── LinkedList.kt
 ├── Main.kt
 ├── MessageUtils.kt
 ├── SplitUtils.kt
 └── StringUtils.kt

Main.kt looks like this:

package org.gradle.sample

fun main() {
 val tokens = StringUtils.split(MessageUtils.getMessage())
println(StringUtils.join(tokens))
}

Where is StringUtils, MessageUtils classes from that directory that have the same package. Why are they available to me? The code compiles and works. I don't import them, and the documentation does not include them in the import by default. Aren't I supposed to import them explicitly?