How does the Maven dependencies flow work?

I am new to Maven so still trying to understand how it works. I have a Project A which is dependent on Random1.jar. Now Random1 is added in dependency of A.
I have project B which is dependent on Project A and also on Random1.jar.
I see my colleague has written something like following :

<dependency>
        <groupId>A</groupId>
        <artifactId>AAAAA</artifactId>
        <version>1.0</version>
        <exclusions>
            <exclusion>
                <groupId>Random1</groupId>
                <artifactId>random1</artifactId>
            </exclusion>
        </exclusions>
    </dependency>
    <dependency>
        <groupId>Random1</groupId>
        <artifactId>random1</artifactId>
        <version>1.0</version>
    </dependency>
</dependencies>

I have not understood why Random1 is excluded from A’s dependency declaration and added again. I checked the version of Random1 in A’s pom and its the same ,i.e 1.0 .